To successfully survive and reproduce, animals must navigate and integrate within broader social and environmental landscapes. House mice (Mus musculus) exhibit complex social structures in the wild, but biomedical research often studies them under impoverished social and spatial conditions that fail to generate core features of wild mouse social organization, such as territoriality. This dissertation examines the intricacies of house mice social organization and the costs and benefits of male territorial competition, with a particular focus on contrasting laboratory and rewilded populations of mice in indoor and outdoor semi-naturalistic contexts. First, I examine the formation of social structures in C57BL/6J (C57) laboratory mice compared to wild-derived outbred mice in outdoor field enclosures. I demonstrate that C57 males form territories less rapidly than wild-derived males, while C57 females explore more and show reduced social preference for familiar same-sex conspecifics. These behavioral differences lead to the formation of distinct social networks between the strains, highlighting the impact of laboratory domestication on mouse social organization. Second, I investigate how social conditions influence the expression of alternative tactics in genetically identical C57 mice. By manipulating population density in outdoor field enclosures, I show that males adopt different strategies depending on their social environment. Males with larger territories invest more in patrolling but are less effective at excluding intruders compared to males with smaller territories. Intruding males, unable to establish territories, adopt an alternative tactic characterized by increased exploration. These alternative behavioral strategies result in differential survival and reproductive access, favoring territory holders. Third, I broaden my comparative approach by examining the spatial, circadian, and social dynamics of Mus pahari, a species that diverged from M. musculus 5-7.6 million years ago. Using a semi-natural indoor arena, I compare M. pahari behavior to that of C57 and wild-derived outbred M. musculus. Our results reveal striking behavioral differences in M. pahari, including reduced spatial exploration, highly stereotyped circadian activity, and enhanced male gregariousness. These findings underscore the genetic basis of social organization within the Mus genus and highlight the potential of M. pahari as a novel model for studying the evolution of social behavior. Collectively, this dissertation provides evidence demonstrating the profound influence of genetic background, domestication processes, social environment, and evolutionary history on mouse social behavior and organization. By bridging laboratory and field approaches, I provide a comprehensive understanding of factors impacting territorial competition and social structure in mice. These insights enhance our knowledge of the lab as a biomedical research model and lay the groundwork for future investigations into the mechanisms underlying strategic social interactions and territorial competition. Finally, this work underscores the importance of natural social contexts in animal behavior studies and opens new avenues for exploring the genetic and neural bases of complex social phenotypes.