The retiring of a number to honor a player likely began with the New York Yankees. The Yankees were not the first team to experiment with numbers on uniforms to identify players, but they were the first to wear numbers permanently and retired Lou Gehrig's number 4 in 1939.

This book covers retired numbers in baseball's major and minor leagues. In the major league section of the book, a player's name is followed by his retired number, the name of the team that retired it, the year that it was retired, the player's primary position, and the teams he was affiliated with during his playing career. The author then presents a brief summary of the player's career and lists any major awards or honors he won. Retiring numbers in the minor leagues is a bit different; a player who excels in the minors isn't usually with a team for long because he is promoted to the majors. In the minor league section, a player's name is followed by a brief summary of his significance. After both the major and minor league sections, readers will find team-by-team and numerical lists of honored players.