Attention-deficit/hyperactivity disorder (ADHD) is a chronic neurodevelopmental disorder that affects 6% of US college students. Young adults with ADHD are less likely to enroll in college and those who do earn significantly lower GPAs. These students are susceptible to a range of adverse outcomes including increased risk-taking, higher rates of criminality, and higher prevalence of comorbid disabilities. One of the most common comorbid conditions of adult ADHD is substance use disorder (SUD) with nearly 30% of those with ADHD diagnosed with a non-alcohol related SUD during their lifetime and 42.7% with an alcohol use disorder. However, substance use does not explain the relationship between ADHD and poorer academic outcomes. Instead, ADHD and substance use confer unique and substantial risks for academic functioning placing college students with ADHD who use substances at a greater, compounded risk, for adverse outcomes. Extant research regarding substance use among college students with ADHD has been primarily drawn from 4-year colleges using cross-sectional designs. Therefore, the current literature base may represent only a snapshot of the highest functioning subgroup of college students with ADHD. There is a critical need to better understand the substance use experiences of all college students with ADHD to reduce harm and promote academic success. A total of 100 first-time first-year college students (50 from 2-year institutions and 50 from 4-year institutions) will be recruited for this study. This project aims to: (a) demonstrate the feasibility of recruiting and retaining first-year college students with ADHD over one-year using responsive ecological momentary assessments, (b) objectively and qualitatively describe the substance use experiences of first-year of college students with rigorously defined ADHD, and (c) identify malleable factors that may inform clinical decision making and future intervention research to prevent or reduce substance use. Results will provide rich preliminary date using both traditional assessment (e.g., interviews, rating scales) and responsive EMA to drive further investigation and inform clinical practice as it relates to preventing or reducing substance use among college students with ADHD at 2- and 4-year institutions. Results will provide the most detailed data regarding substance use among college students with ADHD via response EMA methodology. Second, this study will be the first to detail substance use among college students with ADHD across their first year at 2-year institutions relative to their peers at 4-year institutions and will yield vital information for understanding the needs of these students in settings within which they are most likely to enroll (i.e., 2-year institutions).