The cover picture shows on the right several gallium-containing species as possible intermediates of GaN crystal growth in supercritical ammonia under ammonoacidic conditions. An understanding of the processes of ammonothermal crystal growth is largely lacking, since the underlying chemistry was so far nearly completely unknown. In the left part of the figure, crystals of solid compounds recovered from ammonia are shown, which contain ionic species indicating their presence also in solution under supercritical conditions. Crystal structures and spectroscopic data (background of the right part) afford detailed information on the chemical nature of these species. Details are discussed in the article by R. Niewa et al. on p. 5387 ff. For more on the story behind the cover research, see the Cover Profile.