Abstract: Traditionally, structural biology is studied using techniques such as X-ray crystallography and nuclear magnetic resonance (NMR). Both X-ray crystallography and NMR can solve structures with atomic resolution. Many biomolecules, however, cannot yield qualified crystals for X-ray crystallography, and NMR has limited application for very large biomolecules. Moreover, both techniques require relatively large amounts of samples that may be difficult to obtain in many cases. In recent years, mass spectrometry has emerged as a powerful tool for studies in structural biology, complementary to X-ray crystallography and NMR. In this talk, I would like to present some of our studies on protein complexes, using native mass spectrometry and hydrogen/deuterium exchange mass spectrometry. By using these approaches, we have been able to monitor the behaviour of protein complexes in solutions, to determine the stoichiometry, binding interfaces and conformational changes related to the protein interactions.