This book provides a systematic development of the Rubio de Francia theory of extrapolation, its many generalizations and its applications to one and two-weight norm inequalities.The book is based upon a new and elementary proof of the classical extrapolation theorem that fully develops the power of the Rubio de Francia iteration algorithm.This technique allows us to give a unified presentation of the theory and to give important generalizations to Banach function spaces and to two-weight inequalities.We provide many applications to the classical operators of harmonic analysis to illustrate...