The fourth edition of this important book, which includes additional color illustrations, has been extensively revised, updated, and expanded to reflect the most recent developments. These include advances in patch testing methodology, in particular the new chambers that are appearing on the market, revision of the baseline series of patch tests to reflect the latest evidence-based work, and additional testing procedures. Other additions include sections on key allergens and concentrations, with the result is a superb guide to the current management of positive and negative patch test and prick test reactions that will be invaluable for all practicing dermatologists, from the beginner to the well-trained expert. The fourth edition continues the tradition of partnering with the ICDRG (International Contact Dermatitis Research Group). The ICDRG was formed in 1966 to promote the understanding of contact dermatitis. It has had major roles in the standardization of patch testing and the facilitation of regular scientific meetings, for over forty years and thirty five years respectively. It has also been involved in the authorship of a number of publications on contact dermatitis. Both Drs. Maibach and Lachapelle are members and the ICDRG is now comprised of representatives from all over the world, and currently includes members from Belgium, Sweden, Denmark, the United Kingdom, USA, Germany, Singapore, Korea, India, Japan, Canada, Uruguay and Australia. From the reviews of the previous editions: "The aim is to balance brevity and clarity with sufficient details for beginners in the field of diagnostic patch and prick testing. the book also will be of use to dermatology residents or anyone wishing to gain better knowledge of contact dermatitis. There are many high-quality photographs and useful algorithms and tables. It is clearly and concisely written and will serve asan indispensable guide for any dermatologist interested in contact dermatitis." (Renata H. Mullen, Doodys Review Service, August, 2009).