This book is aimed at future pilots willing to study Electrics and fire protection (021) within the framework of ATPL Theoretical Certificates. It complies with EASA's Learning Objectives for the 021 Certificate. The chapters are all illustrated to facilitate the reader's comprehension. At the end of each chapter, the reader will find key-points highlighting the most important notions. Pierre Le Gleuher is a former student pilot of the ENAC.Laurence Morin is engineer and head of pilot theoretical training at the ENAC. She teaches Airframe, Systems and Electricity to future pilots and engineers at the ENAC.Philippe Rapp is an electronics and electricity engineer. He used to teach Aircraft Electrical Systems to future pilots and Airport Electricity to future electronics engineers at the ENAC. He now works for the Technical Service of French Civil Aviation for energy and airport ground lighting.