Particles and fields : Seventh Mexican Workshop, Mérida, Yucatán, México 10-17 November 1999

This proceedings contains up-to-date reviews on heavy ion physics CP violation, effective lagrangians, experimental techniques, charm hadron production, the physics of electron-proton collisions, and Tevatron physics. A number of short seminars give an overview of the state of the art in particle physics reaching from experimental to phenomenological and theoretical physics.