Additive Manufacturing (AM) of metallic alloys, ceramics and composites often requires a use of prealloyed powders as raw materials. Since synthesizing of such powders is complicated and expensive, an issue of in-situ processing becomes relevant and is increasingly studied nowadays. The main idea of in-situ alloying assisted processing, namely the alloying/reaction occurring between materials of different powders, can be implemented at three principally separate processing stages: pre-processing (raw material preparation), printing itself and post-processing (sintering/infiltration/heat-treatment). The presented brief review gives a necessary background for in-situ alloying at the mostly employed pre-process, process and post-process stages relevant for Powder Bed Fusion (PBF), Direct Energy Deposition (DED) and Binder Jet Printing (BJP) technologies. The presented survey discusses the involved physical processes with their relevance for each mentioned AM technologies and proposes a novel methodology for designing new materials.