Pilot’s Handbook of Aeronautical Knowledge (Federal Aviation Administration)

$5.00 less expensive than any editions currently on the market.
Includes new, updated information from the FAA.
As of 2015, there were 120,546 students studying to be pilots and 600,000 active pilots.
As of 2015, there were 100,993 certified flights instructors (CFIs).
All licensed pilots must pass the FAA Knowledge Exam and Practical Test. This book is authored by the creator of that test in part to help with that test, making this required reading for pilots in training and instructors.