Ἀσέβεια is one of Greek religion's vexatious topics. It was a crime, or γραφή, as well as a religious wrong according to ‘sacred law’. It happened to be the charge in the most famous Greek trial, that of Socrates, and thus became part of a locus classicus, with the result, as Kenneth Dover showed, that later reports of ἀσέβεια trials were often distorted by the influence of Socrates' example. Focussing mostly on the sources found reliable by Dover, this article proposes that ἀσέβεια sometimes resembled μίασμα, which was contagious religious pollution. An impious person could sometimes spread his or her ἀσέβεια, and others could catch it.