We have explored the interactions of mono- and multivalent guests with Recognition-Induced Polymersomes (RIPS) formed from complementary random copolymers featuring diamidopyridine and thymine functionality. Addition of monovalent guests featuring imide functionality to these RIPS induced a temporary swelling of the vesicles, followed by dissociation of the vesicles due to competitive binding of the guest. Conversely, multivalent thymine-functionalized nanoparticle guests were rapidly incorporated into the RIPS, inducing a contraction of RIP diameter over time. These mono- and multivalent interactions were extremely specific: highly analogous control systems showed no interaction with the RIP structures. Taken together, these studies demonstrate highly selective molecular "lock and key" control over higher-order assembly and recognition processes.