This chapter provides readers with an overview of the roles, functions, and knowledge base of counselors and addresses the professional issues that influence the identity and practice of counselors today. The primary role of a counselor is to assist clients in reaching their optimal level of psychosocial functioning through resolving negative patterns, prevention, rehabilitation, and improving quality of life. Rehabilitation counselors work with clients with disabilities and/or chronic illnesses, including those with psychiatric conditions, in settings such as state vocational rehabilitation agencies, hospitals, and so on. Addiction counseling, a recently acknowledged master’s-level counseling specialty, involves working in the substance abuse/addictions field and provides addiction prevention, treatment, recovery support, and education. The shared practice and knowledge domains of counselors and other helping professions coupled with the diversity within the counseling profession has, on the one hand, produced a rich, comprehensive, and inclusive field.