The scale, mechanism, and physiological importance of cuticular transpiration were last reviewed in this journal 5 and 10 years ago. Progress in our basic understanding of the underlying processes and their physiological and structural determinants has remained frustratingly slow ever since. There have been major advances in the quantification of cuticular water permeability of stomata-bearing leaf and fruit surfaces and its dependence on leaf temperature in astomatous surfaces, as well as in our understanding of the respective roles of epicuticular and intracuticular waxes and molecular-scale aqueous pores in its physical control. However, understanding the properties that determine the thousand-fold differences between permeabilities of different cuticles remains a huge challenge. Molecular biology offers unique opportunities to elucidate the relationships between cuticular permeability and structure and chemical composition of cuticles, provided care is taken to quantify the effects of genetic manipulation on cuticular permeability by reliable experimental approaches.