Proteins are encoded in genes in living organisms and play a wide variety of functions in life. X-ray crystallographic technique has provided a solid base for understanding their 3-D architecture. However, relatively little information has been extracted from these studies about their dynamics, because the 3-D structural information is essentially static. In order to understand the mechanistic details of how proteins function, it is crucial to know the dynamics of events that give rise to their designed functions. Recent progress in cryogenic techniques and/or time-resolved X-ray diffraction at synchrotron radiation facilities enables“watching”the collective motions of proteins that closely related to the protein functions. Here I review the instrumentations and feasibility of the protein dynamics research with protein crystallography.