Buddhist monastic law usually divides infractions of precepts into either five or seven groups—the most serious offence of which is known as a pārājika. These are offences of non-celibacy, murder, theft and lying about spiritual attainments. It is generally accepted in the West, where the focus lies on Mainstream or Theravāda Buddhism, that these offences entail permanent expulsion from the monastic order. The present thesis sets out to show that not only do pārājika offences not necessarily entail expulsion, but a monk or nun who transgresses against a pārājika dharma may in fact remain within the saṃgha if his/her transgression was not concealed and if he/she was truly repentant. This procedure is known as pārājika penance. Evidence for this is provided by means of a systematic survey of texts ascribed to five Vinaya traditions, viz. Mahīśāsaka, Sarvāstivāda, Mahāsāṃghika, Dharmaguptaka and Mūlasarvāstivāda. The Vinaya of each of these traditions has been examined and the results produced here in order to shed light on their respective stance with regard to pārājika penance.