There are guidebooks, then there are guidebooks. If you need a general introduction to the incomparable city of Istanbul, giving you an overview of its many and varied attractions, and perhaps helping you choose a hotel or a restaurant or nightclub too, there are several acceptable guides available - the Rough Guide is a fair bet, notwithstanding its inaccuracies.
If, however, you are serious about getting away from the tourist drag and untangling Istanbul's many layers of history, truly getting to know the "real" place and how it has come to be what is today, then this is a book for you. Each of the 23 chapters takes you on foot along a suggested route through the streets and lanes of the Queen of Cities, enabling you to become acquainted with it in a way no other book I'm aware of makes possible. The authors are exceptionally well-informed, and prove themselves able to share their expertise in an intelligent and very readable way, devoting ample space to the countless sites of interest to the visitor without ever becoming tedious. If your particular interest is Byzantine history, or perhaps the Ottoman period, you can easily select which sites to visit - the book makes possible a pick 'n' mix approach to help you. Relevant input from historical and architectural viewpoints enables you to look at familiar locations through new eyes, and even to learn of the existence of sites you never knew existed.
The walks are of varied length, but none of them need take a full day. Plans of key buildings are detailed and appropriate to the text, and route maps are user-friendly minimising the chances of getting lost even in more remote residential areas. The 2009/2010 edition is bang up to date.
Absorb what this book has to offer before your visit, and it will genuinely enhance your experience - and thereby your memories - of Istanbul, a city like no other on earth. "Strolling Through Istanbul" has made available material previously available only in the old Blue Guide, until recently out of print for some years.