This brief, but densely packed book is a must-read in the metaphysics of personal identity. Olson is a fun writer to read, and displays immense skill in the framing and structuring of his argument. Parts I liked: the criticisms of the psychological approach, the constitution view, the bodily criterion, and the chapter 'Was I ever a fetus?' Part I didn't like as much: the casual dismissal of substance dualism, and the section in which he argues that personhood is a phase sortal like adulthood. Still, every part was profitable to read; recommended.