Language impairment (LI) and attention-deficit/hyperactivity disorder (ADHD) are 2 relatively common developmental disorders that have been shown to have high rates of co-occurrence in a number of studies, and this phenomenon is also commonplace in the experience of many clinicians. Understanding this comorbidity, therefore, is central to building coherent taxonomic systems within the field of speech-language pathology for clinical and theoretical reasons. As we review the current literature we consider which models of comorbidity are relevant to the study of LI and ADHD (see Tomblin & Mueller, 2012, for a review of the models that are discussed). Finally, we present original data on the comorbidity of LI and ADHD from a large population-based sample that has been studied over the last 2 decades in the state of Iowa. We evaluate how this contributes to current understanding of these disorders.