This conclusion presents some closing thoughts of key concepts discussed in the preceding chapters of this book. The book describes that twin studies are based on several questionable and outright false theoretical assumptions, and that genetic interpretations of the studies depend on the validity of several assumptions. It begins a five-chapter analysis of TRA studies, with a special emphasis on the classical studies performed by Newman and colleagues, Shields, and Juel-Nielsen. The book examines the controversies surrounding many key concepts and assumptions used in both reared-together and reared-apart twin studies. It focuses on the much more common 'twin method' studies comparing MZT and DZT pairs and on the MISTRA studies of IQ and personality. The book evaluates twin research in psychiatry in the context of over four decades of gene search failures in that field. It attempts to answer the crucial question of whether twin research is good science, uncertain science, or pseudoscience.