Activity theory (AT; Russian: Теория деятельности) is an umbrella term for a line of eclectic social sciences theories and research with its roots in the Soviet psychological activity theory pioneered by Sergei Rubinstein in 1930s. At a later time it was advocated for and popularized by Alexei Leont'ev. Some of the traces of the theory in its inception can also be found in a few works of Lev Vygotsky,. These scholars sought to understand human activities as systemic and socially situated phenomena and to go beyond paradigms of reflexology (the teaching of Vladimir Bekhterev and his followers) and classical conditioning (the teaching of Ivan Pavlov and his school), psychoanalysis and behaviorism. It became one of the major psychological approaches in the former USSR, being widely used in bo