After a short historical sketch of sexual and forensic research in Germany, this chapter will focus on empirical data from a series of studies on 166 sexual murderers in Germany. The studies are mainly based on forensic-psychiatric court reports. High lifetime prevalence rates were found for substance abuse or dependence, paraphilias, especially sexual sadism, and personality disorders (PDs), especially antisocial, borderline, sadistic, and schizoid. In a comparison study with non-homicidal sexual offenders the sexual murderers showed higher rates of sexual sadism as well as PDs, especially schizoid PD. Sexual sadism, voyeurism, and sadistic, antisocial, and schizoid PD were more frequent in the multiple-victim (n = 36) than in the single-victim (n = 130) group. Those offenders who were regarded as having diminished responsibility or being not guilty by reason of insanity, especially those detained in forensic psychiatric hospitals, showed more signs of a progressive sexual sadistic development. Sexual murderers with paraphilias, especially sexual sadism, with antisocial personality traits, and with high scores on risk assessment instruments were less likely to be released from prison or forensic psychiatric hospitals. However, in a follow-up study, neither paraphilias nor PDs predicted sexual recidivism, and only age-related factors (younger age at first sexual offence, at the sexual homicide, and at time of release) were associated with increased violent recidivism. The impact of these findings on the assessment of sexual murderers and future research will be discussed.