Hormone transport in plants is a fundamental process governing all aspects of plant development. Identification and functional analysis of plasma membrane proteins, which regulate the import and export of plant hormones, is a requirement if we are to develop a systems biology level understanding of these processes. For several plant hormones, the characterization of the transporters has produced remarkable steps towards this goal, in particular for auxin transport, where the synthesis of mathematical and laboratory approaches is now being realised. We review current data on the proteins involved in phytohormone transport including discussions of their identity, functional interactions, and kinetic parameters. In particular, for auxin transporters we discuss how expression systems enable us to dissect out the transport mechanisms, and how data from such studies can be combined with mathematical and computational models to develop a systems-based perspective of auxin transport.