Allergic Diseases: Diagnosis and Treatment, 3rd Edition is intended for the “frontline” physician who cares for the allergic patient. We have tried, once again, to make it as “user friendly” and clinically oriented as possible. Our approach to the principles of pathophysiology is intended to allow them to be easily applied to the rationale for therapy. The major intent therefore is still to help the primary care physician deal with the day-to-day management of the allergic patient. The arrangement of this text is similar to that of the first edition, with the major emphasis being on common allergic diseases and the pharmacologic tools we use to control them. To this end two new chapters have been added, one on antihistamines and the other on antileukotrienes. In addition, a new chapter has been added to help the physician deal with the child who experiences recurrent respiratory tract infections. Many of the authors, because of the superb job they did with their first contributions, have been asked for an encore. However, to keep our approach fresh, some of these authors have been asked to write different chapters, and new contributors have been solicited. Regardless of these changes, the thrust of the text remains the same—to disseminate the practical knowledge that we have accumulated in almost 70 years of practice and teaching in the field of allergy and immunology. As with the first and second editions of Allergic Diseases: Diagnosis and Treatment, our greatest hope is that the message has been delivered clearly, effectively, and in a manner that allows its easy application by the physician caring for those who suffer with allergic disease.