Background: Drug delivery systems with nm dimensions (nanoparticles [NPs]) are attracting increasing attention because they can sequester drugs in systemic circulation, prevent non-specific biodistribution, and target to specific tissues. Objective: We reviewed the recent literature pertinent to NP-based drug delivery, primarily emphasizing NPs fabricated from proteins. Methods: A summary of common NP fabrication techniques is provided along with the range of sizes and functional properties obtained. The NP properties critical for injectable drug delivery are reviewed, as well as the attempts to design ‘tissue-specific’ NPs. Results/conclusions: It has been possible to design > 100 nm NPs from different biomaterials, and further understanding of in vivo stability and interactions with physiologic systems will lead to improved drug delivery systems.