The term endophenotype appears to fit the needs of psychiatric genetics, and this concept bridges the gap between the gene and the complexity of psychiatric disease processes. This chapter is organized into two main sections. The first part summarizes representative published studies that have successfully used various endophenotypes to find candidate genes involved in several psychiatric disorders, including schizophrenia, mood disorders, Alzheimer's disease (AD), attention-deficit hyperactivity disorder (ADHD), and suicidal behavior. The second half focuses on alcoholism, and illustrates the successful use of the endophenotype strategy in the Collaborative Study on the Genetics of Alcoholism (COGA) project, where brain oscillations are used as endophenotypes in the identification and understanding of genes involved in alcoholism and related disinhibitory disorders. Endophenotype-based analysis would be useful for establishing a biological underpinning for diagnosis and classification; a net outcome would be improved understanding of the neurobiology and genetics of psychopathology.