The present discussion aims to analyse references concerning Athenian impiety trials in the fifth century BCE up to the well-attested trial of Socrates in 399 BCE. First, it argues that some of the trials must have then been an invention of Hellenistic and later biographers. Second, it analyses the socio-political context of those trials which can be deemed historical. Third, it discusses in detail legal issues connected with such accusations. Overall, it seeks to provide a brief but possibly comprehensive study of Athenian impiety trials in the fifth century BCE, with an article on later trials to follow in one of the next issues of the journal.