This article investigates why homosexual acts are still banned in 77 countries. It extends the current state of research by focusing on the religious roots of these bans. Previous studies have analysed the influence of Islam on prohibitions of same-sex sexual acts but produced contradictory findings. Moreover, the influence of the second world religion that condemns homosexuality in its scriptures – Christianity – has largely been ignored. This article shows that countries with a Muslim tradition tend to criminalise both male and female homosexuality, while predominantly Christian societies tend to prohibit only sex between men. However, the influence of the Christian tradition depends on the modernity of a country: the more modern a Christian society, the less influence traditional Christian sexual ethics have on legislation governing same-sex sexuality. This is particularly true for countries with a Protestant tradition.