Unpredictable and uncontrollable protein adsorption on nanoparticles remains a considerable challenge to achieving effective application of nanotechnologies within biological environments. Nevertheless, engineered nanoparticles offer unprecedented functionality and control in probing and altering biological systems. In this review, we highlight recent advances in harnessing the "protein corona" formed on nanoparticles as a handle to tune functional properties of the protein-nanoparticle complex. Towards this end, we first review nanoparticle properties that influence protein adsorption and design strategies to facilitate selective corona formation, with the corresponding characterization techniques. We next focus on literature detailing corona-mediated functionalities, including stealth to avoid recognition and sequestration while in circulation, targeting of predetermined in vivo locations, and controlled activation once localized to the intended biological compartment. We conclude with a discussion of biocompatibility outcomes for these protein-nanoparticle complexes applied in vivo. While formation of the nanoparticle-corona complex may impede our control over its use for the projected nanobiotechnology application, it concurrently presents an opportunity to create improved protein-nanoparticle architectures by exploiting natural or guiding selective protein adsorption to the nanoparticle surface.