The now-classic article “What Is Temperament? Four Approaches” by H. H. Goldsmith et al. (1987) brought together originators of four prominent temperament theories—Rothbart, Thomas and Chess, Buss and Plomin, and Goldsmith—to address foundational questions about the nature of temperament. This article reviews what has been learned about the nature of temperament in the intervening 25 years, It begins with an updating of the 1987 consensus definition of temperament that integrates more complex current findings. Next, 4 “progeny” trained in the original temperament traditions assess contributions of their respective approaches. The article then poses essential questions for the next generation of research on the fundamentals of temperament, including its structure, links with personality traits, interaction with context, and change and continuity over time.