Colloidal inorganic nanocrystals are promising building blocks for developing novel functional materials due to their ease of fabrication and processing, and the combination of strongly size- and shape-dependent physical properties. Great efforts have been devoted to synthesizing nanocrystals with morphologies of higher complexity in order to uncover greater potential of nanotechnology. In this presentation, we will summarize our recent studies on the production of nanostructures with new morphologies and/or compositions through chemical reactions of pre-formed colloidal inorganic nanocrystals. Hollow nanocrystals of metals, semiconductors, and insulators, and heterogeneous bimetallic dimers will be used as examples to illustrate the processes.