Sylvia Marie Likens (January 3, 1949 – October 26, 1965) was an American teenager who was tortured and murdered by her caregiver, Gertrude Baniszewski, many of Baniszewski's children, and several of their neighborhood friends. The abuse lasted for three months, occurring incrementally, before Likens died from her extensive injuries and malnourishment on October 26, 1965, in Indianapolis, Indiana.

Likens was increasingly tormented, neglected, belittled, sexually humiliated, beaten, starved, lacerated, burned, and dehydrated by her tormentors. Her autopsy showed 150 wounds across her body, including several burns, scald marks and eroded skin. Through intimidation, her younger sister, Jenny, was occasionally forced to participate in her mistreatment. The official cause of her death was determined to be a homicide caused by a combination of subdural hematoma and shock, complicated by severe malnutrition.

Gertrude Baniszewski; her oldest daughter, Paula; her son, John; and two neighborhood youths, Coy Hubbard and Richard Hobbs, were all tried and convicted in May 1966 of neglecting, torturing, and murdering Likens. At the defendants' trial, Deputy Prosecutor Leroy New described the case as "the most diabolical case to ever come before a court or jury" and Gertrude's defense attorney, William C. Erbecker, described Likens as having been subjected to acts of "degradation that you wouldn't commit on a dog" before her death.

After eight hours of deliberation, the jury found Gertrude Baniszewski guilty of first-degree murder. She was sentenced to life imprisonment but was released on parole in 1985. Paula was found guilty of second-degree murder and was released in 1972; Hobbs, Hubbard, and John were found guilty of manslaughter and served less than two years in the Indiana Reformatory before being granted parole on February 27, 1968.

The torture and murder of Sylvia Likens is widely regarded by Indiana citizens as the worst crime ever committed in their state and has been described by a senior investigator in the Indianapolis Police Department as the "most sadistic" case he had ever investigated in the 35 years he served with the Indianapolis Police.