Based on differential equations, game theory, and probability theory, the author discusses mathematical models of metabolic processes, drug metabolism, inheritance under selective pressure, the spread of infection, and the virulence of bacteria, parasites, and viruses. The formulas are derived in detail and in an easily understandable manner, with numerous figures illustrating the explanations. The required mathematical basics are summarized in the appendix. This makes the text suitable for students of biology, medicine, or environmental sciences from their first semesters onward. It is also recommended for mathematicians, physicists, and engineers who wish to familiarize themselves with the modeling of biological processes.