The goal of this book is to characterize the nature of abilities, competencies, and expertise, and to understand the relations among them. The book therefore seeks to integrate into a coherent discipline what formerly have been, to a large extent, three separate disciplines. Such integration makes both theoretical and practical sense, because abilities represent potentials to achieve competencies, and ultimately, expertise. Authors of each chapter (a) present their views on the nature of abilities, competencies, and expertise; (b) present their views on the interrelationships among these three constructs; (c) state their views on how these three constructs can be assessed and developed; (d) present empirical data supporting their position; (e) compare and contrast their position to alternative positions, showing why they believe their position to be preferred; and (f) speculate on the implications of their viewpoint for science, education, and society.