A vacuum pump comprises a first pumping section (106), and, downstream therefrom, a second pumping section (108), The pump comprises a first pump inlet (120) through which fluid can enter the pump and pass through both the first and second pumping sections towards a pump outlet, and a second pump inlet (122) through which fluid can enter the pump and pass through only the second pumping section towards the outlet. The second pumping section (108) comprises an externally threaded rotor (109).