of scientific fields, from electronics to optics, catalysis, biomedicine, energy, etc. Polymer materials and devices that just two decades ago were unimaginable are now being produced, including surfaces with bio-inspired solid adhesion [31], self-operating nanoswimmers [31], photonic [32] or plasmonic antennas [33], whose outstanding properties are derived from their complex nanoscale morphologies. Moreover, the combination of the properties above with the stimuli-responsive properties of polymers offers a route to advanced smart materials, which have the potential to revolutionize the fields of biomedicine, electronics and energy [12; 13; 34; 35; 36; 37; 38; 39; 40]. In addition to allowing for the production of nanostructured polymers, polymerization reactions within spatially restricted spaces can be used to further understand, and in some cases mimic, the synthesis of biopolymers in biological media. Natural polymers are produced by enzymatic catalysis, where stereoselective, regioselective and chemoselective polymerization reactions occur within well-defined nanoscale \"cavities\", which results in tissues with outstanding functionalities [11; 12; 13; 14]. For example, bone tissues exhibit an unusual combination of strength and toughness resulting from a precise selection and organization of materials at the nanoscale: nanometer-sized hydroxyapatite crystals periodically deposit within the gap zones of collagen fibrils, leading to remarkably high elastic modulus along with high energy dissipation and resistance to fracture. Lastly, gaining an understanding of materials' properties at the nanoscale is of undeniable academic and practical interest. It is well-known that physicochemical properties of materials--including polymers--change when the material is confined to the nanoscale, the rationale being that the size of the material comes into conflict with certain characteristic length-scales associated with physicochemical processes [22; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51]. Polymerization in confined geometries therefore allows not only for the investigation of the polymerization reaction itself, but also the production of tailor-made nanoconfined polymers whose physical and chemical properties can be assessed. Two main experimental strategies have been employed to spatially confine polymerization reactions: the use of soft and hard templates. The soft-template strategy utilizes small-molecules which themselves organize into nanoscale cavities within which the polymerization of the monomers occurs. Examples of this approach are the polymerization in micelles, in lipid bilayers, in liquid crystals, in inclusion complexes, etc. [6; 52; 53; 54; 55]. [PERSON] et al., among others, have already addressed polymerizations conducted under soft nanoconfinement, widely demonstrating the feasibility of this approach to fabricate well-defined two- and three-dimensional macromolecular objects, see, e.g., Reference [55] for further details. Our paper will instead report on the state-of-the-art developments on the polymerization within hard AAO templates. According to most of the reported literature, the reduced space of nanoreactors tends to shorten the reaction time and seems to lead to macromolecules of higher molecular weight and/or lower dispersity [56; 57]. Nevertheless, the opposite effect, i.e., a broader molecular weight distribution, has been also reported [58]. In some of these works, mathematical models have been implemented to describe and understand the differences between polymerization in bulk and in confinement in porous nanocavities [59; 60]. The study of polymerization reactions in confined spaces has demanded further investigation and has become the focus of more research over the last few years, due not only to the technological interest in such systems but also because of the need to understand and generalize the complexity of reactions caused by confinement phenomena.