A diffraction image of a crystal taken with an ultrashort pulse of electrons or x-rays provides a snapshot of the material’s momentary atomic structure. We use femtosecond electron pulses in a time-resolved diffraction experiment to record a movie of the structure and motion of the atoms after a short laser pulse deposits energy in the material. In simple words, this experimental technique can be considered as a superfast thermometer measuring the temperature of the crystal’s lattice. The diffraction images contain elastic as well as inelastic scattering signals, which provide detailed information on the vibrational excitations (phonons) and their dynamics. In addition, the flow of energy between electrons and the lattice as well as between different types of phonons can be inferred. We apply this technique to a broad range of inorganic and organic nanoscale solids as well as heterostructures composed of multiple materials.