Jerzy Konorski (1903-1973) exerted a vital influence on the development of physiological psychology and neurobiology. Konorski and his friend and collaborator, Stefan Miller, distinguished instrumental conditioned reflexes as a separate type of acquired behavior, different from classical (Pavlovian) conditioned reflexes. In a series of pioneering studies Konorski demonstrated basic differences between the two types of conditioned reflexes. After the Second World War, he reinterpreted the results of research on conditioned reflexes on the basis of the mechanisms of Sherringtonian neurophysiology and introduced the term plasticity of the nervous system. His work, "Conditioned reflexes and neuron organization", published in 1948, signaled Konorski's place as one of the founders of contemporary neuroscience. He contributed significantly to the understanding of complex interactions of various classes of behaviors: innate and acquired, those driven by opposite motivations, and those elicited by cues signaling different contingencies. In his book "Integrative activity of the brain" (1967), Konorski analyzed the brain as a complex system directing the functioning of the organism as a whole.