This book is concerned with a paradox of immense, potentially life-threatening significance to about 1 in 100 adults and nearly 1 in 10 children, within the European Union. The paradox is that certain nutritious proteins from wholesome foods can act as if they were harmful, sometimes deadly, poisons to otherwise normal people unfortunate enough to possess a food allergy. And, although immunologists have been occupied with the whole problem of allergy throughout the twentieth century, we enter the twenty-first century with a vast number of questions still unanswered. Whilst the lives of food-allergic patients have certainly been improved through the understanding gained so far, an allergic individual is still haunted by the ever-present threat of inadvertent exposure to the allergen – an event that could have devastating consequences. The impact of this constant fear on the lives of caring parents with a food-allergic child, for example, is immense, and can only be appreciated by those who have experienced at first hand the torment involved. There can be no doubt that food allergy is a major, unsolved problem of great economic, social and personal significance. And the problem is getting even worse, because of the current trend in the developed world for an increasing diversity of foods to be routinely available, with an ever-increasing variety of complex recipes and formulations.