MRC is a file format that has become an industry standard in cryo-electron microscopy (cryoEM) and electron tomography (ET), where the result of the technique is a three-dimensional grid of voxels each with a value corresponding to electron density or electric potential. It was developed by the MRC (Medical Research Council, UK) Laboratory of Molecular Biology. In 2014, the format was standardised. The format specification is available on the CCP-EM website.