The phrase "life unworthy of life" (in German: "Lebensunwertes Leben") was a Nazi designation for the segments of the populace which, according to the Nazi regime of the time, had no right to live. It specifically included all Gypsies. Those individuals were targeted to be euthanized by the state, usually through the compulsion or deception of their caretakers. The term included people with serious medical problems and those considered grossly inferior according to the racial policy of Nazi Germany. This concept formed an important component of the ideology of Nazism and eventually helped lead to the Holocaust. It is similar to but more restrictive than the concept of "Untermensch", subhumans, as not all "subhumans" were considered unworthy of life (Slavs, for instance, were deemed useful for slave labor).
The euthanasia program was officially adopted in 1939 and came through the personal decision of Adolf Hitler. It grew in extent and scope from Action T4 ending officially in 1941 when public protests stopped the program, through the Action 14f13 against concentration camp inmates. The euthanasia of people with disabilities continued more discreetly until the end of World War II. The methods used initially at German hospitals such as lethal injections and bottled gas poisoning were expanded to form the basis for the creation of extermination camps where the gas chambers were built from scratch to conduct the extermination of the Jews, and Romani.
The expression first appeared in print via the title of a 1920 book, Die Freigabe der Vernichtung Lebensunwerten Lebens (Allowing the Destruction of Life Unworthy of Life) by two professors, the jurist Karl Binding (retired from the University of Leipzig) and psychiatrist Alfred Hoche from the University of Freiburg. According to Hoche, some living people who were brain damaged, mentally retarded, autistic (though not recognized as such at the time), and psychiatrically ill were "mentally dead", "human ballast" and "empty shells of human beings". Hoche felt killing such people was useful. Some people were simply considered disposable. Later the killing was extended to people considered 'racially impure' or 'racially inferior' according to Nazi thinking.