This article points to the influence of medieval debates about the possible non-existence of a God on the formation of modern atheist discourse. On the basis of sources composed by Muslims, Christians and Jews, alleged appearances of disbelief like apostasy, blasphemy, and immoral behaviour (Epicureanism) are reconsidered. Medieval Latin conceptions of atheism are described as acedia (rejection of and indifference in faith), temptation (non-belief as an experience of crisis), and murmur (protest and non-belief in emergency situations). It is made clear, that doubts or nonbelief in God’s existence were neither rare nor forbidden nor persecuted. Nonbelievers were regarded as fools, rather than as a threat. At the same time, heretics as representatives of opposing teachings were construed as threatening, and indeed persecuted violently in the Latin Christian world and in some Muslim realms.