Book excerpt: A concise, classical approach to the theory of real functions, set in the topological context of metric spaces. Newly translated by G. H. Lawden of the Univ. of Sussex and expanded from the earlier Polish editions to include remarks on the extension of finitely many additive functions to a measure, construction of a continuous, non-differential function of a general type, the Banach-Vitali theorem, and Stepanov's theorem. Prerequisites are set theory, topology, and calculus.