This is a review of the research literature on homicide arrest clearances or homicides for which no offender is arrested. The article describes the decline in the percent of homicides resulting in arrests and charges from over 90 pecent in 1960 to 61 percent in 2006. Research is reviewed on the reasons for the lack of public attention and concern and the low homicide clearance rates in the USA in comparison with other countries. Research on the extent to which homicides are uncleared because they involve low-status persons and those economically disadvantaged is compared with research suggesting that it is the characteristics of the homicide event that make clearance difficult. It seems that such factors as age, gender, and race/ethnicity play a role in whether the homicide is cleared by arrest. Characteristics of homicides that increase clearances include occurrence in private residences, domestic homicides, and homicide with weapons other than firearms. Research on what police can do to increase clearances is examined. Suggestions on how to increase access to information on how homicide investigations are carried out are also discussed.