The psychology of the testimony studies the problems related to the accuracy that a witness shows in the identification. Through a rigorous methodology that has little to do with naïve considerations based on common sense or routine practice, it reaches relatively clear conclusions about the mechanisms and variables that intervene in the testimony. This book introduces an area of study and application very extensive, exposing the scientific criteria that authorize to believe in the truth of a testimony. It is aimed in particular at all those who work in the field of criminal investigation, including legal psychologists, judges, investigators and lawyers.