This article summarizes the most important advances of recent years in the field of gene-environment interaction in allergic response. It specifically examines sensitization to olive pollen as an example of one of the main causes of allergic disease in the Mediterranean area. The presence of at least 20 proteins with allergic activity has been demonstrated in olive pollen, and 10 of these have been characterized (Ole e 1 to Ole e 10). Ole e 1, which is considered to be the majority allergen (causing sensitization in more than 70% of patients), has been the subject of many studies looking for risk factors and ways to protect against sensitization. Markers of the major histocompatibility complex and other genetic loci associated with the allergic response have been analyzed using population-based, family-based, and functional approaches, which have revealed the involvement of genetic regulation in this type of response. Furthermore, evaluation of environmental factors and their relationship with genetic factors is essential when attempting to understand this type of disease. In this review, we provide examples of how exposure to high doses of olive pollen allergen in a specific genetic context can trigger different allergic conditions (from asthma to nonresponse). We stress the importance of evaluating these factors in order to modulate this response correctly.