Genome editing has the potential to transform medicine by replacing DNA sequences associated with disease with non-pathogenic or protective variants. However, major challenges limit the clinical translation of this technology; foremost of which is the difficulty of delivering editing agents to somatic cells in vivo. Many cell types are currently only accessible using viral delivery of DNA encoded editing agents, with inherent packaging size limitations, the likelihood of clinically relevant immunogenicity, and the risk of persistent expression with off-target genome modification and the potential of oncogenic outcomes. Likewise, lipid nanoparticles have little intrinsic cell-type selectivity and have proven difficult to target to specific cells. New delivery technologies are urgently needed that enable selective editing of target cells with high efficiency, while minimizing the duration of exposure to editing agents. We are developing protein polymer-based, cell type-specific delivery systems to enhance the efficacy and safety of genome editors, RNA therapeutics, and other macromolecular cargo for in vivo applications.