libbpm is a C-library which contains low level beam position monitor (BPM) signal processing routines. It's aim is to form a complete set of routines needed to handle RF Cavity BPM data, from digital downmixing, sampling, calibrating analysing and simulating BPM data. This library has been developed in the context of the BPM work done by the accelerator physics groups at University College London, Royal Holloway University of London and the University of Cambridge (UK) (2006-2008)