This paper reviews the development of precision livestock farming, PLF, from the view point of the engineer, farm animal and the farmer. It considers the technological principles upon which PLF is based, gives several examples of PLF, considers which livestock processes are suitable for the PLF approach particularly those affecting animal welfare, addresses whether PLF constitutes technology push or market pull, and stresses the need for a prospective bioethical analysis of PLE We conclude that PLF is an embryonic technology with great promise but one that requires considerable research and development before uptake.