Karl Kautsky in the context of "Social Democratic Labour Party of Georgia"

Orthodox Marxism is the body of Marxist thought which emerged after the deaths of Karl Marx and Friedrich Engels in the late 19th century, expressed in its primary form by Karl Kautsky. Kautsky's views of Marxism dominated the European Marxist movement for two decades, and orthodox Marxism was the official philosophy of the majority of the socialist movement as represented in the Second International until the First World War in 1914, whose outbreak caused Kautsky's influence to wane and brought to prominence the orthodoxy of Vladimir Lenin. Orthodox Marxism aimed to simplify, codify and systematize Marxist method and theory by clarifying perceived ambiguities and contradictions in classical Marxism.

Orthodox Marxism maintained that Marx's historical materialism was a science which revealed the laws of history and proved that the collapse of capitalism and its replacement by socialism were inevitable. The implications of this deterministic view were that history could not be "hurried" and that politically workers and workers' parties must wait for the material economic conditions to be met before the revolutionary transformation of society could take place. For example, this idea saw the Social Democratic Party of Germany (SPD) adopt a gradualist approach, taking advantage of bourgeois parliamentary democracy to improve the lives of workers until capitalism was brought down by its objective internal contradictions.

Christian communism is a theological view that the teachings of Jesus compel Christians to support religious communism. Although there is no universal agreement on the exact dates when communistic ideas and practices in Christianity began, many Christian communists argue that evidence from the Bible suggests that the first Christians, including the Apostles in the New Testament, established their own small communist society in the years following Jesus' death and resurrection. Many advocates of Christian communism and other communists, including Karl Kautsky, argue that it was taught by Jesus and practised by the apostles themselves. This position is also held by historians studying early Christianity.

There are those who hold the view that the early Christian Church, such as the one described in the Acts of the Apostles, was an early form of communism or Christian socialism. The view is that communism was just Christianity in practice and Jesus was the first communist.

The Erfurt Program (German: Erfurter Programm) was the party platform adopted by the Social Democratic Party of Germany (SPD) at its party congress in Erfurt in 1891. Drafted under the political leadership of August Bebel and Wilhelm Liebknecht, and with theorist Karl Kautsky as its principal author, the program officially committed the SPD to Marxism. It was the first and most prominent in a series of similar Marxist-inspired platforms adopted by socialist parties across Europe.

The program represented a stark break from its predecessor, the Gotha Program of 1875, by rejecting the Lassallean idea of achieving socialism through state aid. Instead, it declared the impending death of capitalism and the necessity of class struggle. The program was divided into two parts. The first, the "maximalist" section, outlined the unalterable principles of a socialist transformation based on Marxist theory. The second, "minimalist" section, detailed a series of practical legislative goals to be pursued within the existing framework of the German Empire.