This module introduces two models of the thermal energy budget of a leaf. The reasoning behind the simple, heat energy budget of a leaf is developed in this module into a detailed explanation of leaf transpiration. Typical values for environment variables and leaf parameters are discussed and simple calculations are made to demonstrate how radiation, convection, and transpiration affect leaf temperature. A graphical method of analysis is used to present a more detailed energy budget model. A problem set explores the consequences of the models. Algebra and some knowledge of heat transfer physics are prerequisites.