At least half of all enzyme-catalysed reactions are thought to involve a hydrogen transfer. In the last 10 years, it has become apparent that many of these reactions will occur, in part, or in full, by quantum mechanical tunnelling. We are particularly interested in the role of promoting vibrations on H transfer, and the Old Yellow Enzyme family of flavoproteins has proven to be an excellent model system with which to examine such reactions. In this minireview, we describe new and established experimental methods used to study H-tunnelling in these enzymes and we consider some practical issues important to such studies. The application of these methods has provided strong evidence linking protein dynamics and H-tunnelling in biological systems.