Attention-deficit/hyperactivity disorder (ADHD) is highly prevalent in adults and has been linked to functional difficulties in various life domains, increased risk of other disorders (e.g., depression), and deficits in self-regulation (e.g., time management). My dissertation aims to address a gap in our existing knowledge by identifying patterns of association among ADHD symptoms, co-occurring psychopathology, and life functioning difficulties -- a critical next step to advancing our understanding of diagnosis and treatment of ADHD in adults.