This volume completes the publication of the collected papers of George P?lya, one of the most influential mathematicians and teachers of our time. Volumes I (Singularities of Analytic Functions) and II (Location of Zeros) were published in 1974. Volume IV presents 20 papers on probability, 17 on combinatorics, and 18 on the teaching and learning of mathematics. P?lya has made a number of fundamental contributions to the first two fields, including perhaps the first use of the term "central limit theorem," but his major influence on mathematics has clearly been his approach to pedagogy. Many of the papers throughout these volumes have a strongly pedagogical flavor, but the papers in the third section of this volume focus squarely on the real business of how to do mathematics—how to formulate a problem and then create a solution. This volume is the twenty-third in the series Mathematicians of Our Time, edited by Gian-Carlo Rota.