Common billing codes for mental health services include CPT codes such as 90834 for a 45-minute psychotherapy session, 90837 for a 60-minute session, and 90791 for a psychiatric diagnostic evaluation. ICD-10 codes specify diagnoses, such as F32 for major depressive disorder or F41 for anxiety disorders. Accurate use of these codes by mental health billing experts ensures proper reimbursement and compliance with insurance requirements.