This textbook introduces differential equations, biological applications, and simulations and emphasizes molecular events (biochemistry and enzyme kinetics), excitable systems (neural signals), and small protein and genetic circuits. A Primer on Mathematical Models in Biology will appeal to readers because it grew out of a course that the popular and highly respected applied mathematician Lee Segel taught at the Weizmann Institute and it represents his unique perspective; combines clear and useful mathematical methods with applications that illustrate the power of such tools; and includes many exercises in reasoning, modeling, and simulations.