The study of permeability of plant cuticles is gaining interest since transport processes play a crucial role in plant ecology, plant stress tolerance, plant growth regulation, plant protection, phytopathology and the accumulation of xenobiotics in plants. Penetration of neutral and ionic solutes can be modeled and predicted, provided suitable experiments based on sound theories are conducted using whole leaves, leaf disks or isolated cuticles. These measurements allow estimating water loss from plants, including transgenic plants with an altered cuticle and wax composition. Based on representative examples, the authors describe the basics of sorption, diffusion and permeability characteristics of cuticles. They present suitable experimental approaches, including data analysis, hints to erroneous interpretations and calculations to point out the physiological and ecological consequences.