Fifteen years have passed since the time the Strelau Temperament Inventory (STI) was first published in English (Strelau, 1972a). This questionnaire, aimed at diagnosing the Pavlovian nervous system properties, gained increasing popu­ larity in the West after being published once again (Strelau, 1983) with more information comprising its psychometric characteristics-its construct validity in particular. The aim of this chapter is to present the accumulated results obtained with the STI and to introduce new results based on a broad study conducted on six German samples. In order to show how the STI is related to the Pavlovian theory of nervous system properties, a short introduction into this theory is given.