A new class of molecular transporters—compounds that shepherd drugs and molecular probes such as imaging agents across biological barriers—enters cells more readily than some of the best-performing transporters developed previously. Nearly two decades ago, Paul A. Wender of Stanford University and coworkers discovered that proteins with properly spaced guanidinium surface groups enter cells more readily than other proteins. This led Wender’s group and others to develop many types of cell-penetrating peptides and other molecular transporters to ferry compounds across biological membranes for drug delivery and other applications. Wender, Robert M. Waymouth, and Colin J. McKinlay have now developed oligophosphoesters as molecular transporters (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.5b13452). Compared with oligocarbonates and oligoarginines, two of the best-performing types of molecular transporters, oligophosphoesters move two and six times as much attached cargo, respectively, per unit time. The researchers have filed a patent application on the technology and plan to investigate its use for delivering Taxol to cancer patients.