In this study the possibilities offered by "living" ring-opening metathesis polymerization (ROMP) are exploited to engineer novel macromolecular architectures. It is indeed shown that amphiphilic branched structures of hitherto unreported topologies can be prepared by ROMP of miscellaneous macromonomers, provided the latter polymers carry an end-standing norbornene unsaturation. Janus-type architectures are, for instance, accessible by sequential ROMP of polystyrene (PS) and poly(ethylene oxide) (PEG) macromonomers; other original branched structures, whose topology makes them particularly attractive for applications such as unimolecular micelles or associative thickeners, can be obtained through homopolymerization of macromonomers based on PS-b-PEO diblock copolymers.