Addiction is a chronic-progressive disease marked by phases of relapse and recovery. Patients with moderate to severe addictions typically have mental illness of some form (they are dual-diagnosis patients) reflecting how mental illness and addiction are biologically and bidirectionally causally interlinked. Addiction psychiatrists are formally cross-trained in the diagnosis and treatment of both addiction and mental illness. They conduct diagnostic workups that fully embrace complex addiction–mental illness comorbidities while longitudinally tracking illness evolution and recovery trajectories. As implemented in the 2 × 4 model blueprint of integrated addiction psychiatry care, repeated diagnostic evaluations guide individualized treatment planning that attends to patient’s stages of change while integrating psychotherapeutic, experiential, medication, and/or neuromodulator treatments. Multiple mental illness and addiction subtypes are simultaneously or sequentially targeted over the course of detoxification-withdrawal treatments, harm reduction, and full remission strategies. The advancing frontier of addiction psychiatry will involve the growth of inpatient and outpatient teams composed of addiction psychiatrists, nurses, and therapists that reject fragmented/siloed/split-care models that segregate addiction from mental illness treatment and professional training. Addiction psychiatry teams will be important for researching new integrative treatments in full recognition of addiction and mental illness as highly neurobiologically interconnected and clinically interrelated brain diseases.