The remaining chapters examine recent advances in the research of OCD that could improve diagnostic classification, assessment, and treatment. In the fifth chapter, the possible benefits of a dimensional versus categorical conceptualization of OCD symptoms are examined. A dimensional approach is in line with the most recent call by the National Institute of Mental Health for Research Domain Criteria, which emphasizes the identification of endophenotypic markers across psychopathology. The authors suggest that a dimensional approach would allow for an evolutionary understanding of OCD that could integrate biological and genetic data while allowing for larger sample sizes. Chapters 6, 7, and 8 review the effort to discover endophenotypic markers for OCD through genetic, neurological, and animal research. The final chapter recommends the need for additional cross-cultural and ethnic research on OCD to determine a more reliable and valid diagnostic classification for the disorder.