Historically, the quality of police investigations of police corruption and misconduct has been poor. Numerous police commissions in the United States, Australia, and elsewhere have found major deficiencies when police investigate police. The deficiencies identified have included inadequate planning of investigations, inadequate use of electronic surveillance, failure to interview key witnesses, breaches of confidentiality, and lack of timeliness. A 2001 study of New South Wales (Australia) police internal investigations into serious drug-related police corruption identified a variety of systemic issues. The overall quality of internal investigations was poor and there were too many investigations. There was an emphasis on bureaucratic processing of complaints at the expense of quality driven investigations. An important preliminary step to take in relation to improving the quality of internal affairs investigations is to determine what counts as a good investigation, that is, what constitute the criteria for quality in this area. On the one hand, there is very little in the policing literature on standards for internal investigations. On the other hand, there are various performance indicators in the wider literature on policing that could be applied to internal affairs investigations. This essay focuses on criteria for quality in internal police investigations. In particular, it offers a relatively comprehensive set of criteria for quality in police investigations by professional standards units. Although many of these are straightforward indeed, obvious-they are rarely brought to bear specifically on internal investigations.