 Cell-penetrating peptides provide a highly promising strategy for intracellular drug delivery. One relevant clinical application of cell-penetrating peptides is cancer therapeutics. Peptide-based delivery could increase the uptake of drugs in tumor cells and thereby increase the efficacy of the treatment, either of conventional small molecular drugs or oligonucleotide-based therapeutics. This review is focused on the cancer applications of cell-penetrating peptides as delivery systems. Different aspects of drug loading, cargos and delivery are discussed together with methods for targeted delivery, activatable cell-penetrating peptides and transducable agents coupled to cell-penetrating peptides. This article was authored by Yolo Langell, Arthidas Ramanee, and Jacob Regberg.