The Cinderella effect is a term used to describe the observed, in many but not all studies, significantly higher rate of stepchildren being physically abused, emotionally abused, sexually abused, neglected, murdered, or otherwise mistreated at the hands of stepparents than at the hands of their genetic parents. It takes its name from the fairy tale character Cinderella. The effect has been explained by application of evolutionary psychology theories. There have also been various criticisms of these theories.

In the early 1970s, a theory arose on the connection between stepparents and child maltreatment. "In 1973, forensic psychiatrist P. D. Scott summarized information on a sample of 'fatal battered-baby cases’ perpetrated in anger (…) 15 of the 29 killers – 52% – were stepfathers." Although initially there was no analysis of this raw data, empirical evidence has since been collected on what is now called the Cinderella effect through official records, reports, and census.

For over 30 years, data has been collected regarding the validity of the Cinderella effect, with a wealth of evidence indicating a direct relationship between step-relationships and abuse. This evidence of child abuse and homicide comes from a variety of sources including official reports of child abuse, clinical data, victim reports, and official homicide data. Studies have concluded that "stepchildren in Canada, Great Britain, and the United States indeed incur greatly elevated risk of child maltreatment of various sorts, especially lethal beatings". Studies have found that not biologically related parents are up to a hundred times more likely to kill a child than biological parents.