One of the historical pillars of rehabilitation counseling has been the use of assessment throughout the rehabilitation process. With this historical emphasis, it is not surprising that the focus on assessment and the methods and techniques used have changed and evolved. As a result, students, practitioners, and researchers are on a constant quest for updated and current information to guide and inform practice, policy, and research. This constant quest for updated and comprehensive information is directly relevant to the assessment of individuals typically served by rehabilitation and mental health practitioners and is the focus of this book. To date, there has not been a book that has been able to provide a comprehensive discussion of topics applicable to service delivery across both setting. This book attempts to fill this gap. One factor that guided the development of this book was the authors’ goal to provide both the foundational information necessary to understand and plan the assessment process and combine this material with information that is applicable to specific population and service delivery settings. To achieve this goal, each of the chapters is written by leaders in the field who have specialized knowledge regarding the chapter content. The chapters provide practical hands on information that allows for easy incorporation of the material to rehabilitation and mental health practice. To further strengthen practical application, case studies and templates have been incorporated where applicable to highlight specific key aspects to promote application to service delivery. Second, this is the first assessment book to be developed after the Council on Rehabilitation Counselor Education and Council on the Accreditation of Counseling and Related Programs merger. Finally, the authors hope that the readers of this book can apply this information to enhance the overall quality of life of the individuals they work with, especially individuals with disabilities.