'Marshall's book covers the basic topics with crystal clarity in a style that is conversational and concrete, and that guides the student into thinking about these topics the way a working mathematician does, especially one with a geometric or computational bent. Moreover, the book includes many results that are vital to modern function theory and its applications to geometry, dynamics and probability, but that are often omitted from introductory texts. I wish I had first learned the subject from this book, and I am delighted that my students can do so.' Christopher Bishop, State University of New York at Stony Brook