In this chapter, we summarize psychological research on judgment and decision-making processes in criminal investigations. We start by outlining the nature of investigative tasks and psychological mechanisms with a bearing on those tasks. We then describe relevant reasoning processes in criminal investigations, emphasizing particularly the central roles of narrative construction and hypothesis testing, followed by a description of the psychological underpinnings of common investigative biases and errors. Next, we acknowledge existing and potential measures to improve the quality of investigations and counteract bias, and summarize the empirical research available on this topic to date. In addition, we identify critical gaps in the current literature and propose promising directions for future research.