The use of deep eutectic solvents (DESs) that act as all-in-one solvent–template–reactant systems offers an interesting green alternative to conventional syntheses in materials science. This Review aims to provide a comprehensive overview to emphasize the similarities and discrepancies between DES-assisted and conventional syntheses and rationalize certain green features that are common for the three DES-assisted syntheses described herein: one case of radical polymerization and two cases of polycondensations. For instance, DESs contain the precursor itself and some additional components that either provide certain functionality (e.g., drug delivery and controlled release, or electrical conductivity) to the resulting materials or direct their formation with a particular structure (e.g., hierarchical-type). Moreover, DESs provide a reaction medium, so polymerizations are ultimately carried out in a solventless fashion. This means that DES-assisted syntheses match green chemistry principles 2 and 5 because of the economy of reagents and solvents, whereas the functionality incorporated by the second component allows the need for any post-synthesis derivatization to be minimized or even fully avoided (principle 8). DESs also provide new precursors that favor more efficient polymerization (principle 6) by decreasing the energy input required for reaction progress. Finally, the use of mild reaction conditions in combination with the compositional versatility of DESs, which allows low-toxic components to be selected, is also of interest from the viewpoint of green chemistry because it opens up the way to design biocompatible and/or eco-friendly synthetic methods (principle 3).