This document provides an introduction to fitness principles and testing. It defines physical fitness as the body's ability to function efficiently, consisting of health-related and skill-related components. Health-related components include body composition, aerobic endurance, flexibility, muscular strength and endurance. Skill-related components include speed, agility, balance, coordination and reaction time. It then describes the Physical Activity Pyramid and FITT principles of frequency, intensity, time and type for exercise. Finally, it outlines the Beep Test for measuring aerobic fitness and the Illinois Agility Test for measuring agility.