Compositions, methods, strategies, kits, and systems for the delivery of negatively charged proteins, protein complexes, and fusion proteins, using cationic polymers or lipids are provided. Delivery of proteins into cells can be effected in vivo, ex vivo, or in vitro. Proteins that can be delivered using the compositions, methods, strategies, kits, and systems provided herein include, without limitation, enzymes, transcription factors, genome editing proteins, Cas9 proteins, TALEs, TALENs, nucleases, binding proteins (e.g., ligands, receptors, antibodies, antibody fragments; nucleic acid binding proteins, etc.), structural proteins, and therapeutic proteins (e.g., tumor suppressor proteins, therapeutic enzymes, growth factors, growth factor receptors, transcription factors, proteases, etc.), as well as variants and fusions of such proteins.