Huntington’s disease (HD) causes a combination of motor, cognitive, and psychiatric changes; of these, the behavioral and cognitive aspects cause the greatest disability and have the highest impact on quality of life. The most common and troublesome behavioral problems are depression, suicidal thinking, irritability, apathy, and perseveration. Apathy and perseveration become more common as the disease progresses and correlate with other markers of disease progression, including cognitive impairment, whereas mood changes do not. The most prominent cognitive changes are psychomotor slowing and problems in executive skills and memory. Emotional processing and odor recognition difficulties also occur early. Simple psychomotor measures provide sensitive markers of change, even in premanifest HD, and therefore are crucial in evaluating efficacy of therapeutic interventions. The causes of problem behaviors in HD are complex and reflect an interaction of biologic, social, and environmental factors.