Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder involving functionally disruptive inattentive and/or hyperactive/impulsive behaviors, such as being easily distracted, regularly failing to follow through on tasks, being restless, or often interrupting others. ADHD diagnosed in childhood often persists into adulthood, with 14.6% of U.S. adults meeting the Diagnostic and Statistical Manual of Mental Disorders, 5th ed., criteria for ADHD. When evaluating for adult ADHD, other mental disorders should be included in the differential diagnosis due to the substantial overlap of symptoms and ADHD concurrence with anxiety/stress, mood, personality, impulse control, and substance use disorders. An ADHD diagnosis requires a comprehensive clinical history and evaluation, patient symptom and function assessment (e.g., Adult ADHD Self-Report Scale, Conners Adult ADHD Rating Scales), and gathering of collateral information. Clinical guidelines recommend a subset of amphetamine and methylphenidate stimulants as first-line pharmacotherapy, which may be more effective when combined with psychotherapy. For adults unable to take stimulants or with concurrent anxiety/depression, options include atomoxetine, viloxazine, and bupropion. To monitor for patient misuse or diversion of stimulants, physicians should consider employing controlled substance agreements and prescription drug monitoring programs.