One of the major duties performed by the censors of the Roman Republic was that of the lectio senatus, the enrolment of the Senate. As part of this process they were able to expel from that body anyone whom they deemed unequal to the honour of continued membership. Those expelled were termed ‘praeteriti’. While various aspects of this important and at-times controversial process have attracted scholarly attention, a detailed survey has never been attempted. The work is divided into two major parts. Part I comprises four chapters relating to various aspects of the lectio. Chapter 1 sees a close analysis of the term ‘praeteritus’, shedding fresh light on senatorial demographics and turnover – primarily a demonstration of the correctness of the (minority) view that as early as the third century the quaestorship conveyed automatic membership of the Senate to those who held it. It was not a Sullan innovation. In Ch.2 we calculate that during the period under investigation, c.350 members were expelled. When factoring for life expectancy, this translates to a significant mean lifetime risk of expulsion: c.10%. Also, that mean risk was front-loaded, with praetorians and consulars significantly less likely to be expelled than subpraetorian members. In Ch.3 and 4 we discuss the mechanics of the lectio and review legislative and personal responses to expulsion, including the observations that censors were sensible to a number of societal constraints, among them the opinions of outside actors; also, that expulsion was not necessarily an insuperable setback. Part II comprises a single chapter, a catalogue of all known named praeteriti. An Appendix presents all source testimonia that allude to each praeteritus’ expulsion. The chronological range is bookended by the promulgation of the plebiscitum Ovinium (which gave censors the responsibility of performing the lectio) and the final censorship of the functioning Republic