The upper class in modern societies is the social class composed of the wealthiest members of society, who also wield the greatest political power. The upper class is generally contained within the wealthiest 1-2% of the population, and is distinguished by immense wealth (in the form of estates) which is passed from generation to generation.
Historically in some cultures, members of an upper class often did not have to work for a living, as they were supported by earned or inherited investments (often real estate), although members of the upper class may have had less actual money than merchants. Upper-class status commonly derived from the social position of one's family and not from one's own achievements or wealth. Much of the population that composed the upper class consisted of aristocrats, ruling families, titled people, and religious hierarchs. These people were usually born into their status and historically there was not much movement across class boundaries. This is to say that it was much harder for an individual to move up in class simply because of the structure of society.
thumb|left|Ball in colonial Chile by Pedro Subercaseaux. In Spain's American colonies the upper classes were made up of Europeans and American born Spaniards and were heavily influenced by European trends.In many countries the term "upper class" was intimately associated with hereditary land ownership. Political power was often in the hands of the landowners in many pre-industrial societies despite there being no legal barriers to land ownership for other social classes. Upper-class landowners in Europe were often also members of the titled nobility, though not necessarily: the prevalence of titles of nobility varied widely from country to country. Some upper classes were almost entirely untitled, for example, the Szlachta of the Polish-Lithuanian Commonwealth.
In the United Kingdom, the "upper class" traditionally comprised the aristocracy of "noble" families with hereditary titles. The vast majority of aristocratic families originated in the merchant class, and were ennobled between the 14th and 19th century. Since World War II, the term has come to encompass rich and powerful members of the managerial and professional classes as well.
See main article: American upper class.
In the United States the upper class, also referred to simply as the rich, is often considered to consist of those with great influence and wealth. In this respect the US differs from countries such as the UK where membership of the 'upper class' is also dependent on other factors. The American upper class is estimated to constitute less than 1% of the population, while the remaining 99% of the population lies either within the middle class or working class. The main distinguishing feature of upper class is its ability to derive enormous incomes from wealth through techniques such as investment and money management, rather than engaging in wage-labor or salaried employment.   Successful entrepreneurs, CEOs, politicians, investment bankers, some lawyers and top flight physicians, heirs to fortunes, successful venture capitalists, stockbrokers as well as most celebrities are considered members of this class by contemporary sociologists, such as James Henslin or Dennis Gilbert. There may be prestige differences between different upper-class households. An A-list actor, for example, might not be accorded as much prestige as a former U.S. President, yet all members of this class are so influential and wealthy as to be considered members of the upper class.
While most sociologists define the upper class as the wealthiest 1%, sociologist Leonard Beeghley classifies all households with a net worth of $1 million or more as "rich", while classifying the wealthiest 0.9% as the "super-rich". Since the 1970s income inequality in the United States has been increasing, with the top 1% experiencing significantly larger gains in income than the rest of society.   Social scientists (such as Alan Greenspan) see it as a problem for society, with Greenspan calling it a "very disturbing trend." 
According to the book Who Rules America?, by William Domhoff, the distribution of wealth in America is the primary highlight of the influence of the upper class. The top 1% of Americans own around 34% of the wealth in the U.S. while the bottom 80% own only approximately 16% of the wealth. This large disparity displays the unequal distribution of wealth in America in absolute terms.
. http://sociology.ucsc.edu/whorulesamerica/index.html. Who Rules America: Power, Politics, & Social Change. 5th. McGraw-Hill. 2005. New York. 0-07-287625-5.