New observational signatures of the heating process(es) have been revealed by space missions including SoHO, TRACE, Yohkoh, and RHESSI. Evidences for heating in the quiet corona, active region loops, and the solar wind are different and must be distinguished. Prime indications come from line broadening and waves, the distribution of temperature and radiation loss in relation to height, the correlation of magnetic flux and brightness, nanoflares and other fluctuations. This review concentrates on microevents observed at coronal temperatures. The reported nanoflares in quiet regions are about 2 orders of magnitude smaller than microflares reported in active regions and exhibit less radio emission. To estimate the impact of these microevents on the corona, the effects from a localized energy release must be considered, regardless of the energy source (reconnection or waves). In particular, the coupling with the chromosphere, i.e. the back-reaction of the chromosphere on coronal energy release, has an important effect on the corona. A necessary requirement for the heating process(es) is to deposit most of the heat in the low corona, but to heat also the upper corona to even higher temperature. Finally, the heating process must be able to account for the coronae of more active stars showing coronal emissions at levels of more than 3 orders of magnitude higher than the Sun.