High Quality Content by WIKIPEDIA articles! Activity theory (AT) is a psychological meta-theory, paradigm, or theoretical framework, with its roots in Lev Semyonovich Vygotsky`s cultural-historical psychology. Its founders were Alexei N. Leont`ev (1903-1979), and Sergei Rubinshtein (1889–1960), who sought to understand human activities as complex, socially situated phenomena and go beyond paradigms of cognition, psychoanalysis and behaviorism. It became one of the major psychological approaches in the former USSR, being widely used in both theoretical and applied psychology, in areas such as education, training, ergonomics, and work psychology.