Atopy is triggered by allergens and enhanced by environmental factors, but it has a clear genetic basis, as it is confirmed by the high incidence in siblings and twins. In the last few years, many authors have published genetic studies on asthmatic and atopic patients, generally with very controversial results. In the present article, IgE regulation and other immunological mechanisms which are assumed to be involved in the atopic reaction are reviewed. In the second part, the coding genes of factors, cytokines and receptors that take part in the atopy are commented, as well as review of the recent articles published about genetic markers or polymorphisms associated to these genes. The unveilling of the genetic background of atopy and asthma is a very difficult task, and it will need the definition of a specific atopic phenotype and a clear knowledge of the immunologic basis of atopy. Finally, due to racial and geographical variations a wide collaborative study of many research groups distributed all over the world will be needed.