This long awaited monograph deals with the fascinating group of plants known as geraniums or cranesbills. It is restricted to the plants covered by the scientific name Geranium, but does not include those plants known in English as ?geranium? which botanists have transferred to the genus Pelargonium. The book is the result of 28 years of research by the author. It is lavishly illustrated with maps, line drawings and photographs. There is a gap in the available botanical literatura covering the geraniums. The last monographic treatment by Reinhard Knuth appeared in 1912. In the intervening years, much taxonomic information has been accumulated, rendering this massive and comprehensive work out of date. There have been many new species discoveries and much research has been conducted for revisional works. All these changes have caused much confussion to the outsider, making the need for a comprehensive monograph even more pressing.For each of the 307 species covered in this book, complete synonymy and detailed description is given, as well as its distribution, relationships, variability and taxonomic history are discussed. Each species is provided with a map showing its known distribution based on specimens examined by the author, and is illustrated with line drawings and, if available, with colour photographs based on reliable specimens. Some introductory sections explain in detail the morphological structure of these plants, chromosome numbers, breeding system, phytochemistry, distribution, habitats and relationships. For practical reasons and to facilitate the identification of the species, four identification keys have been prepared that cover respectively North and Central America, South America, the Pacific area and the Old World species. This book will be of value to botanists, but also for specialists hobbyists and to anyone fascinated by these plants.