This book is a part of the Air Transport Pilot’s Licence (ATPL) Course Series provided by the French National University of Civil Aviation (ENAC), describing in detail the mass and balance, flight performance and planning elements of the ATPL course (subject 030). Written by a team of experienced ENAC instructors, it introduces concepts and background knowledge, gradually leading the reader through all relevant sections of the ATPL syllabus. This book is the standard reference for student pilots, instructors and, in addition, meant for those keen on achieving great proficiency in Flight Operations.