Macromonomeric azoinitiators are very special multi-functional polymer molecules which combine the properties of various essential reactants typically used in polymerization reactions in just a single molecule such as polymerizable double bonds and thermolabile azo groups. The reactive groups are typically separated by oligomeric or polymeric chains. For this family of compounds the generic term 'macroinimers' was coined. So, they are initiators, monomers, and crosslinkers and can be beneficially used in all kinds of homo- and copolymerizations to prepare novel polymeric architectures. If the polymerization is carried out in a solvent for the "macro''-part of macroinimers they act in addition as stabilizers for heterophase polymerizations. This review focuses on poly(ethylene glycol) based macroinimers which can be used in aqueous and non-aqueous polymerizations to synthesize branched or hyperbranched crosslinked polymers with macroscopic (monolithic gels) or nanoscopic (nano- or microgel particles) dimensions for potential applications in materials and bio-medical sciences.