Protein drugs delivered via subcutaneous injection represent some of the most promising therapies for a variety of diseases, including treatment of cancer. However, a major challenge for this technology is how to reliably formulate concentrated (>250 mg/ml), low viscosity (i.e., syringeable) solutions of biologically active proteins. Unfortunately, protein drugs often form gels and/or degrade via irreversible aggregation at intermediate protein concentrations of 100-250 mg/ml. In this talk, I describe how proteins can effectively avoid these intermediate concentrations by reversibly assembling into nanoclusters. Nanocluster assembly is achieved by balancing short-ranged, cosolute-induced attractions with weak, longer-ranger electrostatic repulsions near the isoelectric point. Theory predicts that native proteins are stabilized by a self-crowding mechanism within the concentrated environment of the nanoclusters, while weak cluster-cluster interactions can result in colloidally-stable dispersions with moderate viscosities. I present experimental results where this strategy is used to create concentrated antibody dispersions (up to 260 mg/ml) comprising nanoclusters of proteins [monoclonal antibody 1B7, polyclonal sheep Immunoglobin G and bovine serum albumin], which upon dilution in vitro or administration in vivo (mice), dissociate into conformationally stable and biological active protein monomers.