Emerging adulthood is a developmental period where cannabis is used at higher rates compared to other age groups. Social anxiety, a condition defined as being fearful of negative evaluation from others, is also prevalent in emerging adulthood and may be related to cannabis outcomes. Tension reduction theory posits that individuals with social anxiety use cannabis to reduce unpleasant emotions from perceived negative interactions. Research demonstrates that social anxiety and cannabis are related in adulthood; however, the literature in emerging adulthood is mixed. The overarching goal of this dissertation was to elucidate the association between social anxiety and cannabis outcomes in emerging adulthood by (a) quantifying the strength of the association between social anxiety and cannabis outcomes in the extant literature and (b) examining contributing factors to this association. Study 1 (k = 18) used meta-analytic methods to establish the magnitude of the associations between social anxiety and cannabis-related variables. Results supported a small significant (but negligible) positive association between social anxiety and cannabis problems, but not cannabis use frequency, in emerging adulthood. Study 2 (N = 5,194) used epidemiological data from a nationally representative sample in the United States to explore what sociodemographics and psychiatric disorders may be associated with co-occurring social anxiety disorder (SAD) and cannabis use in emerging adults. Results revealed that being White, a part-time student, or not a student were associated with increased odds of having co-occurring lifetime cannabis use and SAD. Additionally, having major depressive disorder, bipolar I disorder, generalized anxiety disorder, specific phobia, agoraphobia, and panic disorder were associated with increased odds of having co-occurring lifetime cannabis use and SAD. Study 3 (N = 269) used a mediated moderation to test negative urgency and sex as moderators that may strengthen the associations between social anxiety and cannabis outcomes in emerging adults. Results revealed that higher social anxiety predicted elevated cannabis use and problems via coping motives, but only for males higher in negative urgency. Overall, this work expanded our understanding of the associations between social anxiety and cannabis outcomes among emerging adults. Results have implications for informing screening approaches in this population.