The informal reading inventory is a diagnostic instrument used by learning disability specialists, reading teachers, and classroom teachers to identify an appropriate reading grade level placement for students, and to identify strengths and weaknesses in word recognition and comprehension. In recent years, a number of studies have examined its validity and reliability. This article gives a comprehensive review of this research. Based on the findings of this review, suggestions of ways the teacher can improve the validity and reliability of existing informal reading inventories are provided, along with suggestions for evaluating reliability and validity of newly published IRI's.