The shortening of the periods of detention for treatment, deterrence or retribution have made a live issue of whether (or when) it is justifiable to detain violent and sexual offenders solely for the protection of others. Anti-protectionist arguments have made ‘dangerousness' a dirty word, but are based either on actuarial statistics of doubtful relevance or on confused moral reasoning. A typology of ‘dangerousness' is tentatively offered, and the impossibility of adequately supervising some dangerous offenders in the community is emphasised. That said, offenders detained solely for the sake of others are entitled to more than merely ‘humane containment’.