This review addresses the fabrication and properties of novel polyelectrolyte microcapsules, with an emphasis on their mechanical and permeability properties. Ease of preparation through layer-by-layer self assembly, accurate control over wall thickness as well as flexibility in the choice of constituents make these capsules very promising for numerous applications in materials and life science. Moreover, by engineering the inner and outer interfaces, these capsules can be used as microreactors for precipitation, crystallization, and polymerization reactions, as well as enzymatic, and heterogeneous catalysis.