This article presents masculinity as a dynamic risk factor in offences of violence between men. It argues that existing interventions into such violence, in prison, hospital and community settings may be enhanced by incorporating masculinity as a dynamic risk factor alongside other dynamic risk factors such as difficulties in anger management, social skills deficits or problems in moral reasoning. Masculinity is defined as a common denominator of men, as men, across social divisions, as opposed to existing approaches to men's identity, as men, which employ the concept of different 'masculinities' being produced by men in different social positions. The latter approach, while useful in terms of discovering men's personal identity, may be less useful in terms of explaining commonality between men, across other axes of social identity, and consequent broad patterns of violence between men. The development of masculinity as a dynamic risk factor depends on isolating masculinity from other axes of men's identity. It is argued that the individual man may demonstrate his masculinity by two categories of violence to other men: violence which includes victims in the category 'man' as worthy rivals and violence which excludes victims from the category 'man' as unworthy of being there. Masculinity as a dynamic risk factor in man to man violence is developed with particular reference to racism and homophobia.