The increasing importance of nanotechnology in the biomedical field and the recent progress of nanomedicines into clinical testing have spurred the development of even more sophisticated nanoscale drug carriers. Current nanocarriers can successfully target cells, release their cargo in response to stimuli, and selectively deliver drugs. More sophisticated nanoscale carriers should evolve into fully integrated vehicles with more complex capabilities. First, they should be able to sense targets inside the body and adapt their functions based on these targets. Such devices will also have processing capabilities, modulating their properties and functions in response to internal or external stimuli. Finally, they will direct their function to the aimed site through both subcellular targeting and delivery of loaded drugs. These nanoscale, multifunctional drug carriers are defined here as nanodevices. Through the integration of various imaging elements into their design, the nanodevices can be made visible, which is an essential feature for the validation. The visualization of nanodevices also facilitates their use in the clinic: clinicians can observe the effectiveness of the devices and gain insights into both the disease progression and the therapeutic response. Nanodevices with this dual diagnostic and therapeutic function are called theranostic nanodevices. In this Account, we describe various challenges to be overcome in the development of smart nanodevices based on supramolecular assemblies of engineered block copolymers. In particular, we focus on polymeric micelles. Polymeric micelles have recently received considerable attention as a promising vehicle for drug delivery, and researchers are currently investigating several micellar formulations in preclinical and clinical studies. By engineering the constituent block copolymers to produce polymeric micelles that integrate multiple smart functionalities, we and other researchers are developing nanodevices with favorable clinical properties.