Soviet historiography is the way in which history was and is written by scholars of the Soviet Union. The major factor which influenced the work of Soviet historians was strict control by the authorities aimed at propaganda of the Communist ideology and Soviet power.
It was declared that the October Revolution had opened a new epoch of the human civilization   . The "class struggle" and the history of Communist Party led by Lenin became the overarching themes of Soviet historiography 
At the 20th Congress of the Communist Party of the Soviet Union in 1956 Khrushchev denouncing Stalin opened the door for some level of scholarship although constraints and dogmas on the Communist party as vanguard of the working class still had to be observed. It became possible to mention in a pejorative context the non-persons like Leon Trotsky and Grigory Zinoviev. Khrushchev decoupled Lenin and Stalin that allowed Soviet historians to produce books and articles of more diversity than during the Stalin era. The reform in history writing was referred to as the return to Leninist norms. 
The era of Brezhnev was the time of samizdat (circulating unofficial manuscripts within the USSR) and tamizdat (illegal publication of work abroad). The three most prominent Soviet dissidents of that era were Alexandr Solzhenitsyn, Andrei Sakaharov and Roy Medvedev. Of the tamizdat authors, Solzhenitsyn was the most famous, publishing his Gulag Atchipeligo in the West in 1973. Medvedev's Let History Judge: The Origins and Consequences of Stalinism was published in 1971 in the West. Neither could publish in the Soviet Union until the advent of Perestroika and Glasnost.
Soviet historiography had been severely criticized by scholars, chiefly — but not only — outside Soviet Union, with its very status as scholarly called into question, and described as ideology and pseudoscience. In particular, Robert Conquest concluded that 
All in all, unprecedented terror must seem necessary to ideologically motivated attempts to transform society massively and speedily, against its natural possibilities. The accompanying falsifications took place, and on a barely credible scale, in every sphere. Real facts, real statistics, disappeared into the realm of fantasy. History, including the History of the Communist Party, or rather especially the history of the Communist Party, was rewritten. Unpersons disappeared from the official record. A new past, as well as new present, was imposed on the captive minds of the Soviet population, as was, of course, admitted when truth emerged in the late 1980s".
That criticism stems from the fact that in the Soviet Union, science was far from independent. Since the late 1930s, Soviet historiography treated the party line and reality as one and the same. As such, if it was a science - it was a science in service of a specific political and ideological agenda, commonly employing historical revisionism. In the 1930s, historic archives were closed, original research severely restricted. Historians were required to pepper their works with references — appropriate or not — to Stalin and other "Marxist-Leninist classics", and to pass judgment — as prescribed by the Party — on pre-revolution historic Russian figures.
The state-approved history was openly subjected to politics and propaganda, similar to philosophy, art, and many fields of scientific research. The Party could not be proven wrong, it was infallible and reality was to conform to this line. Any non-conformist history had to be erased, and questioning of the official history was illegal.
Many works of Western historians were forbidden or censored, many areas of history were also forbidden for research as, officially, they never happened. As such, it remained mostly outside the international historiography of the period. Translations of foreign historiography were often produced in a truncated form, accompanied with extensive censorship and corrective footnotes. For example, in the Russian 1976 translation of Basil Liddell Hart's History of the Second World War pre-war purges of Red Army officers, the secret protocol to the Molotov-Ribbentrop Pact, many details of the Winter War, the occupation of the Baltic states, the Soviet occupation of Bessarabia and Northern Bukovina, Allied assistance to the Soviet Union during the war, many other Western Allies' efforts, the Soviet leadership's mistakes and failures, criticism of the Soviet Union and other content were censored out.
The official version of Soviet history has been dramatically changed after every major governmental shake-up. Previous leaders were always denounced as "enemies", whereas current leaders were usually a subject of a personality cult. Textbooks were rewritten periodically, with figures - such as Lev Trotsky or Stalin himself - disappearing from their pages or being turned from great figures to great villains.
Certain regions and periods of history were made unreliable for political reasons. Entire historical events could be erased, if they did not fit the party line. For example, until 1989 the Soviet leadership and historians, unlike their Western colleagues, had denied the existence of a secret protocol to the Soviet-German Molotov-Ribbentrop Pact of 1939, and as a result the Soviet approach to the study of the Soviet-German relations before 1941 and the origins of World War II were remarkably flawed. In another example, the Soviet invasion of Poland in 1939 as well as the Polish-Soviet War of 1919-1920 were censored out or minimized from most publications, and research suppressed, in order to enforce the policy of 'Polish-Soviet friendship'. Similarly, the enforced collectivisation, the wholesale deportations or massacres of small nationalities in the Caucasus or the disappearance of the Crimean Tatars are not recognized as facts worth of mention. Soviet historians also engaged in producing false claims and falsification of history, for example Soviet historiography falsely claimed that Katyn massacre was carried out by Germans rather than by Soviets as was the case. Yet another example is related to the case of Soviet reprisals against former Soviet POWs returning from Germany; some of them were treated as traitors and imprisoned in GULAGs for many years, yet that policy was denied or minimized by Soviet historians for decades and modern Western scholars have noted that "In the past, Soviet historians engaged for the most part in a disinformation campaign about the extent of the prisoner-of-war problem."
A major factor influencing unreliability of Soviet historiography was that the Soviet interpretation of Marxism predetermined much of the research done by historians. Due to that, Soviet historians could not offer non-Marxist explanations for their theories, even on occasions where other theories fit the reality much better.  The creation of the Soviet Union was presented as the most important turning event in the human history, based on the Marxist theory of historical materialism. This theory identified means of production as chief determinants of the historical process. They led to the creation of social classes, and class struggle was the 'motor' of history. The sociocultural evolution of societies had to progress inevitably from slavery, through feudalism and capitalism to communism. Furthermore, the Communist Party became the protagonist of history, as a "vanguard of the working class", according to development of this theory by Lenin. Hence the unlimited powers of the Communist Party leaders were claimed to be as infallible and inevitable as the history itself  . It also followed that a world-wide victory of communist countries is inevitable. All research had to be based on those assumptions and could not diverge in its findings.
The Marxist bias has been also criticized, for example, for assigning to the Roman rebellions the characteristics of the social revolution, or for errors in comparing the recent developments in Russia with those in the Western countries (for example, Soviet Union mostly "skipped" the period of capitalism required by Marxist theory before the period of communism can be reached). 
Often, the Marxist bias and propaganda demands mixed: hence the peasant rebellions against the early Soviet rule were simply ignored - as inconvenient politically and contradicting the Marxist theories.
The quality (accuracy and reliability) of data published in the Soviet Union and used in historical research is another issue raised by various Sovietologists.  The Marxist theoreticians of the Party considered statistics as a social science; hence many applications of statistical mathematics were curtailed, particularly during the Stalin's era. Under central planning, nothing could occur by accident. Law of large numbers or the idea of random deviation were decreed as "false theories". Statistical journals were closed; World renown statisticians like Andrey Kolmogorov or Eugen Slutsky abandoned statistical research.
As with all Soviet historiography, reliability of Soviet statistical data varied from period to period. The first revolutionary decade and the period of Stalin's dictatorship both appear highly problematic with regards to statistical reliability; very little statistical data were published from 1936 to 1956 and  The reliability of data has improved after 1956 when some missing data was published and Soviet experts themselves published some adjusted data for the Stalin's era; however the quality of documentation has deteriorated.
While some researchers say that on occasion statistical data useful in historical research (such as economical data invented to prove the successes of the Soviet industrialization, or some published numbers of Gulag prisoners and terror victims as Conquest claims) might have been completely invented by the Soviet authorities , there is little evidence that most statistics were significantly affected by falsification or insertion of false data with the intent to confound the West. Data was however falsified both during collection - by local authorities who would be judged by the central authorities based on whether their figures reflected the central economy prescriptions - and by internal propaganda, with its goal to portray the Soviet state in most positive light to its very citizens.  Nonetheless the policy of not publishing - or simply not collecting - data that was deemed unsuitable for various reasons was much more common than simple falsification; hence there are many gaps in Soviet statistical data. Inadequate or lacking documentation for much of Soviet statistical data is also a significant problem.  
A number of specific claims made by Soviet historians and supported by some of their Western colleagues have been described as examples of big lie by historians Robert Conquest and Richard Pipes. The examples of alleged fallacies on their part included the following:
Deliberately false historical narratives were used in concert with repressions, often as fundamental basis for legal theories produced by Soviet courts and security organs. For example, as one of the supposed reasons in systematic elimination of the pre-occupation government ministers of Republic of Estonia was proposed the idea that the legitimate post-Russian Empire government of Estonia had been Bolshevik, which had been illegally overthrown by reactionaries with support from foreign armies. On this basis, anybody who had been working in a state offic before occupation could be convicted of "anti-Soviet activities".
Not all areas of Soviet historiography were equally affected by the ideological sturdiness of the regime's, which in any case varied considerably over time. The degree of the ideologization of different areas of historic science varied as well. The worst was situation with history of 19th and, especially of 20th centuries. Therefore, despite part of the Soviet historiography being affected by extreme ideological bias, and compromised by the deliberate distortions and omissions, it has produced a large body of significant scholarship which continues to be used in the modern research. For example, Soviet works on Byzantium, created and published in Soviet Union, are held in high regard.
Mikhail Pokrovsky (1862-1932) was held in highest repute as a historian in the Soviet Union and was elected to the Soviet Academy of Sciences in 1929. He emphasized Marxist theory, downplaying the role of personality in favour of economics as the driving force of history. However, posthumously, Pokrovsky was accused of "vulgar sociologism", and his books were banned. After Stalin's death, and the subsequent renouncement of his policies during the Khrushchev Thaw, Pokrovsky's work regained some influence.
A new book published in Russia in 2006, entitled “A Modern History of Russia: 1945-2006: A Manual for History Teachers” has received significant attention after being publicly endorsed by Russian President Vladimir Putin at a conference for history teachers. On that occasion, Putin said that "we can't allow anyone to impose a sense of guilt on us," and that the new manual helps present a more balanced view of Russian history than that promoted by the West. The book acknowledges the repressions carried out by Stalin and others, but argues that they were "a necessary evil in response to a cold war started by America against the Soviet Union." It cites a recent opinion poll in Russia that gave Stalin an approval rating of 47%, and states that "The Soviet Union was not a democracy, but it was an example for millions of people around the world of the best and fairest society."
According to The Economist magazine, the promotion of this book by a Russian President represents a revival of certain themes prevalent in Soviet historiography, most notably the idea that "Russia's past was admirable, its present is more than magnificent and as for its future—it is beyond anything that the boldest mind can imagine" (first articulated by Count Alexander Benckendorff in the 1830s). The Economist magazine further contends that the book is inspired by Soviet historiography in its treatment of the Cold War, as it claims that the Cold War was started by the United States, that the Soviet Union was acting in self-defence, and that the USSR did not lose the Cold War but rather voluntarily ended it. According to The Economist, "rabid anti-Westernism is the leitmotif of [the book's] ideology." 
Soviet system, including the practice of rewriting history by Soviet historiography era were used as inspiration by George Orwell for the Ministry of Truth and other concepts in his classic dystopian novel, Nineteen Eighty-Four, as well as for his other work, the Animal Farm. 
Viktor Suvorov, in his book "The Liberators",  satirized Soviet historiography by claiming it could be used to show that every Soviet leader was a traitor. For instance, Suvorov wrote that "Vladimir Lenin was an enemy", because all his friends were proven to be "enemies of the people" by the Soviet courts, which are the most democratic and just in the world. These "enemies" were Leon Trotsky, Nikolai Bukharin, Alexei Rykov, and Karl Radek. It was Lenin who brought these "wrecklers" to power, said Suvorov, so that brave chekists had to kill them all with bullets or ice axes. "Stalin was also an enemy", "as has been proven to the entire world at the historical 20th Congress of the Communist Party". Of course, "Stalin himself destroyed thousands of enemies and spies from his closest surrounding, but he could not exterminate them all", so that his "closest friend Lavrenty Beria and his notorious gang have been executed only after Stalin". Sadly enough, continued Suvorov, Khrushev, who got rid of Beria, turned out to be a traitor, just like his successor Leonid Brezhnev, who was guilty of terrible corruption.