The objective of this monograph is to provide an overview of the scope of allergic disorders, and review the current understanding of the mechanism of the allergic response. Due to the extensive nature of the topic, we will limit our discussion to systemic reactions eliciting an IgE-mediated response. Further, the intimate relationship between organs involved will be reviewed, particularly the relationship between allergic rhinitis and asthma. Part I includes the current evaluation, including historical features, exposures, physical exam findings, and ancillary diagnostic options will be reviewed.