The term "informed clinical opinion" appears in the regulatory requirements for the implementation of Part C of the Individuals with Disabilities Education Act (IDEA) as an integral part of an eligibility determination. It must be included in evaluation and assessment procedures, since it is a necessary safeguard against eligibility determination based upon isolated information or test scores alone. Since the term carries different meanings for individuals and agencies, it is important to clarify the meaning and use of "informed clinical opinion" in the context of Part C. This document uses a question-and-answer format to address three key issues: (1) What does informed clinical opinion mean in the context of Part C? (2) How does informed clinical opinion affect the determination of eligibility? and (3) Why is it necessary to document informed clinical opinion? The paper reprints Part C regulations pertaining to informed clinical opinion and includes one reference. (Author/SG)