In the past decades, polymer based nanoscale polymeric assemblies have attracted continuous interest due to their potential applications in many fields, such as nanomedicine. Many efforts have been dedicated to tailoring the three-dimensional architecture and the placement of functional groups at well-defined positions within the polymeric assemblies, aiming to augment their function. To achieve such goals, in one way, novel polymeric building blocks can be designed by controlled living polymerization methodology and advanced chemical modifications. In contrast, by focusing on the end function, others and we have been practicing strategies of cooperative self-assembly of multiple polymeric building blocks chosen from the vast library of conventional block polymers which are easily available. The advantages of such strategies lie in the simplicity of the preparation process and versatile choice of the constituent polymers in terms of their chemical structure and functionality as well as the fact that cooperative self-assembly based on supramolecular interactions offers elegant and energy-efficient bottom-up strategies. Combination of these principles has been exploited to optimize the architecture of polymeric assemblies with improved function, to impart new functionality into micelles and to realize polymeric nanocomplexes exhibiting functional integration, similar to some natural systems like artificial viruses, molecular chaperones, multiple enzyme systems, and so forth. In this Account, we shall first summarize several straightforward designing principles with which cooperative assembly of multiple polymeric building blocks can be implemented, aiming to construct polymeric nanoassemblies with hierarchal structure and enhanced functionalities. Next, examples will be discussed to demonstrate the possibility to create multifunctional nanoparticles by combination of the designing principles and judiciously choosing of the building blocks. We focus on multifunctional nanoparticles which can partially address challenges widely existing in nanomedicine such as long blood circulation, efficient cellular uptake, and controllable release of payloads. Finally, bioactive polymeric assemblies, which have certain functions closely mimicking those of some natural systems, will be used to conceive the concept of functional integration.