Sexual homicide (or sexual murder) is broadly defined as a homicide with an apparent or underlying sexual motivation. Most research on sexual homicide has involved population studies of single serial (SSHOs) or single-victim sexual homicide offenders (SVSHOs). However, little empirical knowledge is available on the differences between SSHOs and SVSHOs. This chapter reviews five published empirical studies that distinguish the offender, victim, and offense characteristics of SSHOs and SVSHOs. Before outlining the major differences between these two groups of sexual murderers, the chapter first outlines the prevalence and theoretical explanations of sexual homicide offending, then discusses differences in the modus operandi of SSHO and non-serial sexual homicide offenders who perpetrated sexual assaults and homicides independently. The chapter concludes with a discussion of limitations and suggestions for further research to inform both research and practice in this field.