The subject of real analysis is unified in this modern text by several central concepts, in particular the notion of absolute continuity. Absolute continuity, a major underlying idea in formulating and proving the Fundamental Theorem of Calculus (FTC), the Lebesgue Dominated Convergence Theorem, and the Radon--Nikodym Theorem, is essential in dealing with problems of switching limits and of understanding the amazing inverse relationship between integration and differentiation (FTC). Also, it leads to fundamental notions and results in terms of weak convergence of measures, a topic generally not treated in standard real variable texts. The topics are examined in depth and in a way that is valuable not only from a theoretical point of view, but in a way that presents a sophisticated array of tools with which to deal with a host of difficult practical problems.