(from the chapter) Philosophers (e.g., Kant, 1790) and psychologists traditionally separate traits (i.e., relatively stable and transsituational sources of individual differences) into three major categories: affective, cognitive, and conative traits. Affective traits are personality characteristics (such as need for achievement, neuroticism, conscientiousness). Cognitive traits include traditional concepts of broad abilities (such as intelligence), narrower ability constructs (e.g., verbal comprehension, math ability), and even more narrow abilities and skills (reaction time to simple stimuli and typing speed). Conative or volitional traits include motivation and interests. More generally, conation is characterized as will. For much of the twentieth century, with a few notable exceptions, researchers were typically concerned with only a single category of traits, such as personality or abilities, and there were relatively few studies of the interactions between and interrelations among these different categories of traits. In the last two decades, this kind of isolated research has been augmented by investigations of how these different categories of traits relate to one another. In this chapter, I will briefly review some of these streams of integrative research. First, however, a few general considerations and qualifications are needed.