Following his retirement from the Army, Grossman founded the Killology Research Group to educate law enforcement officers and soldiers how to improve outcomes in lethal encounters. Grossman is best known for his police training program, based on the self-coined study of "killology", which aims to reduce officers' psychological inhibition to kill suspects. Grossman describes a facet of his training as it relates to the human reluctance to kill as "making it possible for people to kill without conscious thought."