Time resolved crystallography utilizes X-ray crystallography imaging to visualize reactions in four dimensions (x, y, z and time). This enables the studies of dynamical changes that occur in for example enzymes during their catalysis. The time dimension is incorporated by triggering the reaction of interest in the crystal prior to X-ray exposure, and then collecting the diffraction patterns at different time delays. In order to study these dynamical properties of macromolecules three criteria must be met; 
* The macromolecule must be biologically active in the crystalline state
* It must be possible to trigger the reaction in the crystal 
* The intermediate of interest must be detectable, i.e. it must have a reasonable amount of concentration in the crystal (preferably over 25%). 
This has led to the development of several techniques that can be divided into two groups, the pump-probe method and diffusion-trapping methods.