Laurence Leonard is one of the most prolific and well-respected researchers in the area of specific language impairment (SLI) in children, and he is well qualified to write a book surveying the topic. SLI is a disorder of unknown origin, which appears to have a genetic component, causing delays and disorders of language development in children of normal nonverbal intelligence with no significant medical, emotional, or sensory deficits. The primary purpose of this book is to provide a comprehensive review of research in the field of SLI, and Leonard has the minute knowledge necessary to succeed at the task. The coverage in the book reaches back to the earliest nineteenth-century descriptions of children who fit the profile and then moves forward quickly to the massive literature that has accumulated on the topic in the last 20 years. Following the introductory historical and definitional section, Leonard goes on to describe the nature of the linguistic impairment in SLI, including important cross-linguistic accounts and nonlinguistic cognitive issues. The book also covers hypotheses of causation, in a “nature versus nurture” section, and clinical issues of assessment and intervention. Part V, on theory, may be of most interest to psycholinguists who are not language disorders specialists. Overall, there is no doubt that this book is both an excellent introduction for those unfamiliar with SLI and a welcome overview and resource for experts. Leonard's knowledge is encyclopedic, his presentation erudite, and his grasp of detail unfailingly impressive.