Throughout history, incarceration of offenders was used only as a pretrial and presentence detention measure. In the latter part of the 18th century, imprisonment became itself a form of punishment for convicted criminals, although with moralistic overtones. Already in the 1800's, however, practitioners of the fledgling science of criminology were challenging prisons as failures even in terms of their limited objectives. At the same time, progressive penologists in some countries (e.g., the United States, Australia, Ireland) were trying to go beyond the custodial functions of prisons, experimenting with work release, supervised liberty, and commutation of sentences for good behavior as alternatives to systematic incarceration as the only means of crime and offender control. Correctional practices progressed from exploitation of inmates' work as slave labor to moral improvement concepts (e.g., the Philadelphia penological school) to current emphasis on treatment, rehabilitation, and social reintegration of convicted offenders. Penologists and criminologists of different ideological persuasions agree that imprisonment destroys and corrupts individuals guilty of minor offenses, while reinforcing the criminal traits of hardened and violent offenders. Current penological movements include reform, reductionism, and abolitionism. Supporters of correctional reforms and of the reductionist philosophy (the latter advocating reduced sentences for all but the most incorrigible and dangerous criminals) are about equal in numbers. Only radical criminologists advocate the total abolition of imprisonment for all criminals, whose existence they refuse to admit. Some criminologists have reacted with alarm to an alleged conterreform in the corrections field since some countries have imprisoned terrorists in maximum security facilities. These are, however, exceptional measures dictated by emergency situations and by public demands for effective repression of escalating political violence. Centripetal tendencies toward imprisonment with traditional implications of solitary confinement, iron bars, high walls, and maximum security are being increasingly replaced by centrifugal practices which include all possible alternatives to imprisonment in all countries of the world, whether socialist or capitalist. -- in Spanish.