This paper reviews the theory and reseach of the Warsaw school of individual differences, which have modified the typological model constracted by neo-Pavlovian school. Strelau has conceptualized temperament and personality in a different way from the theory postulated by the neo-Pavlovian typology. Strelau has developed a temperament inventory (STI) to measure excitatory and inhibitory strength, the equilibrium of these processes, and the mobility of nervous processes.