Cryogenic electron microscopy in materials science. Cryogenic transmission electron microscopy (cryo-TEM) is simply transmission electron microscopy conducted on specimens that are cooled in the microscope. The ability to probe chemistry, structure, and bonding on the atomic scale in the temperature range from a few Kelvin to room temperature in structural and functional materials in a variable temperature transmission electron microscope is an intriguing prospect that will open up many new areas of materials research. The articles in this issue of MRS Bulletin explore the current capabilities, future developments, and opportunities for cryogenic electron microscopy in materials science. The cover shows (top) a cryo-TEM reconstruction of a polyhedral wireframe DNA nanoparticle with a designed octahedral shape (Courtesy of H. Jun et al., ACS Nano 13, 2083 [2019]); (right) a nanoscale magnetic structure of individual magnetic monopoles in an artifi cially frustrated 2D square spin-ice lattice (Courtesy of C. Phatak et al. Phys. Rev. B 83, 174431 [2011]); and (left) a simultaneously acquired cryo-STEM electron energy-loss spectroscopy map (Courtesy of M. Zachman). See the technical theme that begins on p. 924.