The concept of masculinity does not sit alone but is understood in relation to notions of femininity within the broader concept of "gender" or the structure of gender relations. This is the way in which the social environment constructs men and women's social positioning with reference to assumptions around embedded gender defined roles and traits and attaches specific values and ideas to frequently unquestioned, societal gender hierarchies, or socially accepted gendered norms (Connell 2005; Kimmel 2000). Masculinity, although affiliated to the male body, is therefore interlinked with idealized beliefs and discourses around what "men should be like" or what men naturally are like (Duriesmith 2016, p. 27; Flood 2002). Relationally, this is supported by theories of what women naturally are and should be and typically built around gender binaries such as men as active, public, and strong and women as passive, private, and weak (Cohn 2013). These beliefs and assumptions about the natural condition of men and masculinity impact upon the male sense of identity, which is then reproduced in gendered social action. The association of masculinity with conflict is complex. Cultural and social understandings of masculinity typically place men as more violent and with a greater affiliation to war-making institutions such as the military. Although it is recognized that there is not one type of masculinity and that masculinities are changeable and contested, assumption around what it means to be a man have very real consequences for the practices of conflict. Taking masculinity seriously helps us understand better why conflict takes place, how conflict is fought, who is impacted, and in what way. This entry covers areas of subtopics in the masculinity and conflict literature such as hegemonic masculinity, military masculinities, and the role of masculinity in wartime violence and sexual violence. Also covered are some areas of newer research that examines alternative masculinities in non-state armed groups, peacebuilder masculinities and the notion of the "new man" masculinity.