Colloidal inorganic nanocrystals (NCs) are among the most exploited nanomaterials to date due to their extreme versatility. Research on NCs went through much advancement in the last fifteen years, for example in the synthesis, which opened up the possibility to control their size, shape and topology in chemical composition. An additional step forward was the creation of a wide range of superstructures from the assembly of such NCs, which can be thought of as new types of artificial solids. This, coupled with the possibility to replace the native ligands on the surface of the NCs with shorter molecules, down to single atom ligands, has conferred unique electrical features to films of NCs that make them attractive for low cost alternatives to many technologies. Progress also came from the study of chemical transformations in nanostructures, most notably via cation exchange, which involves replacement of the sublattice of cations in a crystal with a new sublattice of different cations, while the sublattice of anions remains in place. Also, a new field of study has emerged recently, aiming at investigating the transformations in colloidal synthesized nanomaterials under conditions like thermal annealing and/or irradiation. In part this research is boosted by the recent availability of microscopy tools by which one can follow the transformations on individual NCs in-situ, i.e. when such perturbations are actually applied to the sample. The present lecture will highlight the recent progress (with emphasis on the contributions from our group) in the study of chemical and structural transformations in NCs.