When it first appeared, in Germany i 1970 and in Britain in 1971, this books sparked off the greatest theological debate since the Second Vatican Council and finally caused the author to lose his licence from the church to teach. However, the question is still far from being settled: on the contrary, events of recent times from Pope John Paul II's nomination of bishops and statements on birth control to the publication of a world catechism and 'Veritatis Splendor' show that it has become an even ore urgent one. Long unavailable, 'Infallible?' now reappears with a new preface by Gerbert Gaaf and a survey of the discussion.