This module is used to introduce the biology student to differential calculus, a branch of mathematics that is often used in ecological and physiological models. Since biological systems are dynamic, their mathematical models must describe rates of change of relevant variables, a process which requires calculus. The module introduces modeling in biology by reviewing differential calculus and using only examples from life sciences. A problem set reviews information in the text proper and presents additional information not included in the text. The module uses computer programming to graphically check the user’s own calculations and to demonstrate the validity of general solutions.