Bidding the fourth suit can be problematic to many bridge players. This may be because beginners' text-books make only cursory reference to it, and more advanced books take it for granted that the reader understands it. This book, aimed at intermediate to advanced players, seeks to fill that gap. It explains why a bid of the fourth suit is such an important element of the auction, when to bid the fourth suit, what a fourth-suit bid shows in different situations and how to continue the auction. As well as discussing the basic principles, the book contains numerous example deals showing these principles in action, many taken from World Championship matches involving world-class partnerships. The contents proceed in a logical manner, starting with the simplest applications of fourth-suit bidding theory and then moving gradually through more complex situations. The result is a detailed and comprehensive account of practically all the fourth-suit bidding sequences anyone is likely to encounter at the bridge table. This new (2022) edition has been expanded to include additional up-to-the-minute theoretical material as well as some clarifications and updates of existing ideas. More example deals showing the use of the fourth suit in practice have been added, and for ease of reference an index of bidding sequences has been included . This edition also contains a number of quizzes which will allow the reader to test their understanding of the concepts. This will give them the confidence to approach their next session feeling fully prepared for the battle ahead. The author is a contributor of theoretical articles to various bridge magazines, including "The Bridge World" (USA), and "Bridge Magazine" (UK). He learnt to play bridge as a teenager and showed sufficient aptitude for the game to win the England Schools championship some eighteen months later. A mere half-century later, he has participated in trials to represent England Seniors in the home internationals.