Police corruption involves criminal or improper behavior by police officers for personal gain. It undermines the criminal justice system and public trust in the police. There are different types of corruption like accepting gratuities, taking bribes, theft, and protecting illegal activities. Corruption can range from a few "rotten apples" to being widespread and organized in a police department. Theories for why it occurs include individual officer explanations, neighborhood factors, and police subculture and organization issues. Controlling corruption requires internal police mechanisms like effective leadership and supervision as well as external oversight like investigations and public scrutiny.