An overview of the wide range of polymer-based capsules that have been constructed from synthetic and biological building blocks or from biological building blocks that are taken out of their natural environment, using both hyperbranched and self-assembly approaches, was reviewed. The capsules that are discussed can be considered as the simplest mimics of an organelle or cell and contain a cavity in which chemical reactions can take place or cargo can be stored. The chemical tool box available for constructing polymer micelles and polymersomes is much larger, and natural motifs have been actively incorporated into their designs. Regarding LbL, polymersome, or polymeric micelle nanoreactors, it can be predicted that nature's biocatalysts will be increasingly used for encapsulation in these synthetic systems, holding promise for future nanoscale diagnostic devices. One of the main challenges in this field will be the effective stimulation of responsive polymersomes since most stimuli reported thus far cannot be applied in living organisms.