Describes the importance of a focused and comprehensive assessment in developing a clinically valuable case conceptualization and treatment plan. Distinguishes diagnostic assessment from pattern-based and theory-based assessment (e.g., ACT, CBT, and Brief Dynamic). Specifies the clinical value of a comprehensive assessment in developing an effective case conceptualization. Then, it distinguishes standard assessment from case conceptualization–based assessment. A case example, with interview transcription, illustrates a case conceptualization–based assessment.