 Cell-penetrating peptides, CPPs, are small molecules that can enter cells through their cell membranes. They are typically used as carriers for drugs or other cargo that cannot pass through the cell membrane. However, CPPs often become stuck inside the endosome, which is a compartment within the cell where materials are taken up from outside the cell. To overcome this problem, researchers have developed methods to help CPPs exit the endosome and enter the cytoplasm. These include using multiple copies of CPPs on a single molecule, activating CPPs with acidic conditions found in endosomes, and using CPPs attached to chromophores that can be triggered by light. This article was authored by Jean-Philippe Pellois, Ting-Yi Wang, Ryan Baker, and others.