This chapter provides three case studies. These case studies are used throughout the upcoming chapters. They will help readers understand how specific psychological assessment instruments can be used with persons presenting with concerns similar to the case study examples and how alike presenting persons may score on psychological assessment instruments. Second, the chapter succinctly describes the two primary diagnostic classification systems used by counselors in the United States. These include the Diagnostic and Statistical Manual of Mental Disorders-5 (DSM-5-TR) and the International Classification of Diseases (ICD-10). Third, the chapter helps readers gain a general understanding of typical assessment intake interviews. Next, the authors describe the purpose and major components included within counseling progress notes. Finally, the chapter provides an overview of three common progress note taking methods.