Are people more or less depressed in larger cities? Are attention spans shorter in busy urban areas? Urban Psychology is the study of how the built environment of cities influences human behavior and causes psychological adaptations at the individual level. In this dissertation, I present research extending Urban Scaling Theory models to better understand how cities shape human psychology. I discuss (1) an application of these models to reveal how cities systematically influence the risk of psychological depression, (2) an extension of these models to understand how heterogeneous interactions in cities influence implicit racial bias levels and economic outputs, and (3) evidence that selective attention capabilities are increased in larger cities. These studies are first forays into Urban Psychology research and pave the way for future projects that aim to determine the interplay between individual and neighborhood characteristics and average behaviors for entire urban areas. My hope is that the field of urban psychology brings more psychological focus to understanding how cities’ complex physical and social environments constrain behavior through regularities of human mobility but also provide a greater diversity of social and economic experiential options. Doing so will hopefully lead to new discoveries in terms of understanding human behavior and the inner workings of large-scale complex systems.