Welcome to The Mathematical Playground, a book celebrating more than thirty years of the problems column in the MAA undergraduate magazine, Math Horizons. Anecdotes, interviews, and historical sketches accompany the puzzles, conveying the vibrancy of the “Playground” community. The lively prose and humor used throughout the book reveal the enthusiasm and playfulness that have become the column's hallmark. Each chapter features a theme that helps illustrate community: from the Opening Acts—chronicling how interesting questions snowball into original research—to the Posers and Solvers themselves. These stories add an engaging dimension beyond the ample mathematical challenge. A particular highlight is a chapter introducing the seven editors who have produced “The Playground”, revealing the perspectives of the individuals behind the column. The Mathematical Playground has plenty to offer both novice and experienced solvers. The lighthearted, conversational style, together with copious hints, a problem-solving primer, and a detailed glossary, welcomes newcomers, regardless of their background, to the puzzle-solving world. The more seasoned solver will find over twenty new problems plus open-ended challenges and suggestions for further investigation. Whether you're a long-time Math Horizons reader, or encountering “The Playground” for the first time, you are invited into this celebration of the rich culture of recreational mathematics. Just remember the most important rule … Have fun!