Second Life (SL) is a virtual world developed by Linden Lab that launched on June 23, 2003 and is accessible via the Internet. A free client program called the Second Life Viewer enables its users, called Residents, to interact with each other through avatars. Residents can explore, meet other residents, socialize, participate in individual and group activities, and create and trade virtual property and services with one another, or travel throughout the world, which residents refer to as the grid. Second Life caters for users aged over eighteen, while its sister site Teen Second Life is restricted to users aged between thirteen and eighteen.
Built into the software is a three dimensional modeling tool based around simple geometric shapes that allows a resident to build virtual objects. This can be used in combination with the Linden Scripting Language which can be used to add functionality to objects. More complex three dimensional Sculpted prims (colloquially known as sculpties), textures for clothing or other objects, and animations and gestures can be created using external software. The Second Life Terms of Service ensure that users retain copyright for any content they create, and the server and client provide simple digital rights management functions.
Second Life has an internal currency, the Linden dollar (L$). L$ can be used to buy, sell, rent or trade land or goods and services with other users. Virtual goods include buildings, vehicles, devices of all kinds, animations, clothing, skin, hair, jewelry, flora and fauna, and works of art. Services include "camping", wage labor, business management, entertainment and custom content creation. L$ can be purchased with fiat currency from Linden Lab, independent brokers or other users. Money obtained from currency sales is most commonly used to pay Second Life's own subscription and tier fees; only a relatively small number of users earn large amount of money from the world. (In December 2006, a Reuters article stated that the majority of profitable businesses made less than $10 a month, and 90% made less than $200 a month.)
Some companies generate US dollar earnings from services provided in Second Life. Examples are Languagelife.com, Rivers Run Red and Beta Technologies. This opportunity is extending to normal residents and non-Second Life users via affiliate programs. The total value of these transactions has not been calculated but in 2008 consultancy firms Rivers Run Red and Electric Sheep have reported annual revenues of $6 million.
In 2008, Second Life was honored at the 59th Annual Technology & Engineering Emmy Awards for advancing the development of online sites with user-generated content. Philip Rosedale, President of Linden Lab, accepted the award.
Philip Rosedale formed Linden Lab in 1999. His initial focus was on the development of hardware that would enable computer users to be fully immersed in a three hundred and sixty degree virtual world experience. In its earliest form, the company struggled to produce a commercial version of the hardware, known as "The Rig", which was realized in prototype form as a clunky steel contraption with several computer monitors that users could wear on their shoulders. That vision soon morphed into the software application Linden World, in which users could participate in task based games and socialization in a three dimensional online environment. That effort would eventually transform into the better known, user centered Second Life.
Although he was familiar with the metaverse of Neal Stephenson's novel Snow Crash, Rosedale has said that his vision of virtual worlds predates that book, and that he conducted some early virtual world experiments during his college years at the University of California San Diego, where he studied physics.
At the beginning of September 2008, just over 15 million accounts were registered, although there are no reliable figures for actual long term consistent usage. In January 2008 residents spent a total of 28,274,505 hours "inworld", and, on average, 38,000 residents were logged in at any particular moment. Second Life has several competitors, including Entropia Universe, IMVU, There, Active Worlds, Kaneva, and the erotically oriented Red Light Center.
Cory Ondrejka, who helped program Second Life, resigned as chief technology officer on December 11, 2007. On March 14, 2008, Philip Rosedale announced plans to step down from his position as Linden Lab CEO and to become chairman of Linden Lab's board of directors. Rosedale announced Mark Kingdon as the new CEO effective May 15, 2008.
On July 8, 2008, Mitch Kapor, the chairman of the board of Linden Labs, sparked controversy with his keynote speech at the Second Life in world fifth birthday celebration by apparently disparaging the current user base of Second Life;
During a 2001 meeting with investors, Rosedale noticed that the participants were particularly responsive to the collaborative, creative potential of Second Life. As a result, the initial objective driven, gaming focus of Second Life was shifted to a more user created, community driven experience. 
Second Life's status as a virtual world, a computer game, or a talker, is frequently debated. Unlike a traditional computer game, Second Life does not have a designated objective, nor traditional game play mechanics or rules. As it does not have any stipulated goals it is irrelevant to talk about winning or losing in relation to Second Life. Likewise, unlike a traditional talker, Second Life contains an extensive world that can be explored and interacted with, and it can be used purely as a creative toolset if the user so chooses. However, the vast majority of users use Second Life primarily as an entertainment medium, and for most of them the ability to interact with other users is critical to that. "Clubs" where users engage in generic chat, and sexually themed areas, are consistently the most populated.
See main article: Resident (Second Life).
There is no charge to create a Second Life account or for making use of the world for any period of time. Linden Lab reserves the right to charge for the creation of large numbers of multiple accounts for a single person but at present does not do so. A Premium membership (US$9.95 per month) facilitates access to an increased level of technical support, and provides a stipend of L$300/week.
Avatars may take any form the user chooses, animal, vegetable or mineral, including being made to resemble the person whom they represent. A single Resident account may have only one avatar at a time, although the appearance of this avatar can change between as many different forms as the Resident wishes. A single person may also have multiple accounts, and thus appear to be multiple Residents (a person's multiple accounts are referred to as alts).
Avatars can communicate via local chat or global instant messaging (known as IM). Chatting is used for localized public conversations between two or more avatars, and is visible to any avatar within a given distance. IMs are used for private conversations, either between two avatars, or among the members of a group, or even between objects and avatars. Unlike chatting, IM communication does not depend on the participants being within a certain distance of each other. As of version 188.8.131.52, voice chat, both local and IM, is also available on both the main grid and teen grid, using technology licensed by Vivox, a provider of similar services to other MMO worlds.
Instant Messages may optionally be sent to a Resident's email when the Resident is logged off, although message length is limited to 4096 bytes.
In 2007, Brazil became the first country to have its own independently run portal to Second Life, operated by an intermediary - although the actual Second Life grid accessed through the Brazilian portal is the same as that used by the rest of the worldwide customer base. The portal, called "Mainland Brazil", is run by Kaizen Games, making Kaizen the first partner in Linden's "Global Provider Program". In October 2007, Linden Lab signed a second "Global Provider Program" with T-Entertainment Co., LTD., Seoul, Korea and T-Entertainment's portal called "SERA Korea" serves as a gateway to Second Life Grid. Previously, starting in late 2005, Linden Lab had opened and run their own welcome area portals and regions for German, Korean and Japanese language speakers.
Public chat within the world supports many different written languages and character sets, providing the ability for people to chat in their native language. Several resident-created translation devices provide machine translation of public chat (using various online translation services), allowing for easy communication between residents that speak different languages.
See main article: Real estate (Second Life).
Premium membership allows the Resident to own land, with the first 512m² free of the usual monthly Land Use Fee (referred to by residents as Tier, because it is charged in tiers). There is no upper limit on tier; at the highest level, the user pays US$195 for their first 65536m², and then US$97.50 per each additional 32768m² of land. Any land must first be purchased from either Linden Lab or a private seller. There are four types of land regions; Mainland, Private Region, Homestead and Openspace. A region comprises an area of 65536m² (16.1943 acres) in area, being 256 meters on each side. Mainland regions form one continuous land mass, while Private regions are islands. Openspace regions may be either Mainland or Private, but have lower prim limits and traffic use levels than Mainland regions. The owners of a Private region enjoy access to some additional controls that are not available to mainland owners, for example they have a greater ability to alter the shape of the land. Residents must own a region (either Mainland or Private) to qualify for purchasing an Openspace region.
Linden Lab usually sells only complete 65536m² (16.1943 acres) regions at auction (although smaller parcels are auctioned on occasion, typically land parcels abandoned by users who have left). Once a Resident buys land they may resell it freely and use it for any purpose that it is not prohibited by the Second Life Terms of Service.
Residents may also choose to purchase, or rent, land from another Resident (a Resident landlord) rather than from Linden Lab. On a Private region, the built in land selling controls allow the landlord to sell land in the region to another Resident while still retaining some control. Residents purchasing, or renting, land from any other party than Linden Lab are not required to hold a Premium membership nor to necessarily pay a Tier fee, although typically the landlord will require some form of upfront and/or monthly fee to compensate them for their liability to pay the Land Use Fee charged by Linden Lab. However Linden Lab acknowledges only the landlord as the owner of the land, and will not intervene in disputes between Residents. This means, for example, that a landlord can withdraw a Resident's land from availability, without refunding their money, and Linden Lab will not arbitrate in the dispute.
|Free||Sign Up, Avatar Creation, Login ID, Access, Participation|
|US$1||266 Linden Dollars (variable) - brokered purchase; may go to LL or a resident seller|
|US$0.30||per transaction fee for buying Linden Dollars on Lindex currency exchange|
|3.5% of transaction value||per transaction fee for selling Linden Dollars on Lindex currency exchange|
|US$9.99/month||Premium membership (512 m² mainland, access to higher mainland ranges as below, 300 Linden Dollars per week, access to live and ticket support)|
|US$125/month||Land as below, plus Concierge service (live support access)|
|US$100||Island interuser transfer (includes relocation and renaming)|
|US$500 plus 20 premium memberships||Unique avatar surname for an organization|
|Monthly Land Fee||Additional Land||Parcel Size (m2)||Max Prims|
|US$5||1/128 Mainland Region||512||117|
|US$8||1/64 Mainland Region||1024||234|
|US$15||1/32 Mainland Region||2048||468|
|US$25||1/16 Mainland Region||4096||937|
|US$40||1/8 Mainland Region||8192||1875|
|US$75||1/4 Mainland Region||16,384||3750|
|US$125||1/2 Mainland Region||32,768||7500|
|US$195||1 Mainland Region||65,536||15,000|
|+US$95||+1/2 Mainland Region (when already at US$195 level)||32,768||7500|
|US$195||Private Island on pre-2007 server technology (second hand purchase only)||65,536||15,000|
|US$295||Private Island on current server technology||65,536||15,000|
For Mainland fees, the fee determines only the area of land available; the number of prims available is determined by the land itself. The values shown above are the norm but some rare mainland regions offer more prims in the same land area. For non-mainland fees, the fee sets both the land area and the prim count.
Second Life comprises the viewer (also known as the client) executing on the user's personal computer, and several thousand servers operated by Linden Lab.
Linden Lab provides official viewers for Microsoft Windows 2000 / XP, Mac OS X, and most distributions of Linux. A third-party version is available for Solaris and OpenSolaris. Since the viewer is open source,  users may recompile it to create their own custom viewers; modified viewer software is available from third parties. The most popular is the Nicholaz Edition; this viewer, produced by Nicholaz Beresford, includes bug fixes developed outside Linden Lab that are not yet included in the Linden Lab code. The Electric Sheep Company has introduced the OnRez Viewer, which makes substantial changes to the design of the user interface. ShoopedLife is a Second Life client that generates randomized hardware details and sends them to the Second Life server as part of the login, rendering the user anonymous, save for their IP address.
An independent project, libsecondlife, offers a function library for interacting with Second Life servers. libsecondlife has been used to create non-graphic third party viewers, including SLEEK, a text browser using.NET, and Ajaxlife, a text viewer that runs in a web browser and TextSL  a text client inspired by the Zork adventure game that allows visually impaired to access Second Life using a Screenreader.
In February 2008 a partnership between Linden Lab and Vollee was announced. In May, Vollee launched an open Beta trial for a Second Life mobile application that lets Residents travel and communicate in-world by logging in from a handset using an existing account. The service, introduced for free, requires downloading a thin client to a 3G or Wi-Fi enabled handset.
A special beta client is available, which is updated very regularly, and is used for constant software testing by volunteers. The beta client connects to a "beta grid" which consists of a limited number of regions mirrored at regular intervals from the real grid. The mirroring process overwrites any changes made on the beta grid, and thus actions taken within it are not stored by the servers; it is for testing purposes only. Every few months, the standard software is replaced by the beta-grid software, intended as a big upgrade. The Second Life user-base is growing rapidly, and this has stimulated both social and technological changes to the world; the addition of new features also provides periodic boosts to the growth of the economy.
Each region in the Second Life "grid" runs on a single core of a multi-core server, running proprietary software based on Debian. These servers run scripts in the region, as well as providing communication between avatars and objects present in the region.
Every item in the Second Life universe is referred to as an asset. This includes the shapes of the 3D objects known as primitives, the digital images referred to as textures that decorate primitives, digitized audio clips, avatar shape and appearance, avatar skin textures, LSL scripts, information written on notecards, and so on. Each asset is referenced with a universally unique identifier or UUID.
Assets are stored on Isilon Systems storage clusters, comprising all data that has ever been created by anyone who has been in the SL world. Infrequently used assets are offloaded to S3 bulk storage., the total storage was estimated to consume 100 terabytes of server capacity. The asset servers function independently of the region simulators, though the region simulators request object data from the asset servers when a new object loads into the simulator.
Each server instance runs a physics simulation to manage the collisions and interactions of all objects in that region. Objects can be nonphysical and non moving, or actively physical and movable. Complex shapes may be linked together in groups of up to 255 separate primitives. Additionally, each player's avatar is treated as a physical object so that it may interact with physical objects in the world., Second Life simulators use the Havok 4 physics engine for all in-world dynamics. This engine is capable of simulating thousands of physical objects at once.
Linden Lab pursues the use of open standards technologies, and uses free and open source software such as Apache, MySQL and Squid. The plan is to move everything to open standards by standardizing the Second Life protocol. Cory Ondrejka, former CTO of Second Life, has stated that a while after everything has been standardized, both the client and the server will be released as free and open source software.
See main article: OpenSimulator.
In January 2007, OpenSimulator was founded as an open source simulator project. The aim of this project is to develop a full open source server software for Second Life clients. OpenSIM is BSD Licensed and it is written in C# and can run under Mono environment. The community is fast growing and there are some existing alternative Second Life grids which are using OpenSimulator.
See main article: Criticism of Second Life.
In 2006, attorney Marc Bragg initiated a lawsuit against Linden Lab, claiming that they had illegally deprived him of access to his account after he discovered a loophole in the online land auction system which allowed regions to be purchased at prices below reserve. Although most users and commentators believed that Bragg would have no chance of winning, a number of legal developments occurred as a result of the case, including a court ruling that parts of the Second Life Terms of Service were unenforceable, due to being an unconscionable contract of adhesion. The case eventually ended with Bragg's land and account being restored to him in a confidential out-of-court settlement. As such, a settlement created no precedent and thus left users with confusion as to what legal rights they truly had with respect to their virtual land, items, and account. Many of Bragg's legal arguments rested on the claim—advertised on Linden Lab web site—that virtual land within Second Life could be "owned" by the purchasing user, which was removed shortly after the settlement, leading to speculation that this was part of the reason for the settlement.
In the past, large portions of the Second Life economy comprised businesses that are now regulated or banned. Changes to Second Life's Terms of Service in this regard have largely had the purpose of bringing activity within Second Life into compliance with various international laws, even though the person running the business may be in full compliance with the law in his own country. Typically, Linden Lab offer no compensation for businesses that are damaged or destroyed by these rule changes, which can render significant expenditure or effort worthless.
On July 26, 2007, Linden Lab announced a ban on in-world gambling, in fear that new regulations on internet gambling could affect Linden Lab if it was permitted to continue. The ban was immediately met with in-world protests.
In August 2007, a $750,000 in-world bank called Ginko Financial collapsed due to a bank run triggered by Linden Lab's ban on gambling, which halved the size of the Second Life economy. The aftershocks of this collapse caused severe liquidity problems for other virtual "banks," which critics had long asserted were scams. On Tuesday, January 8, 2008 Linden Lab announced the upcoming prohibition of payment of fixed interest on cash deposits in unregulated banking activities in-world. All banks without real-world charters closed or converted to virtual joint stock companies on January 22, 2008. After the ban, a few companies continue to offer non-interest bearing deposit accounts to residents, such as the e-commerce site OnRez, and Ancapistan Capital Exchange, which had already adopted a zero-interest policy three months prior to the LL interest ban.
Due to Second Life's rapid growth rate, it has suffered from difficulties related to system instability. These include system lag, and intermittent client crashes. However, more disturbing faults are caused by the system's use of an "asset server" cluster, on which the actual data governing objects is stored separately from the areas of the world and the avatars that use those objects. The communication between the main servers and the asset cluster appears to constitute a bottleneck which frequently causes problems.