Determining the best methods of assessment for a library instruction program in a large research university can be a challenging task. Albert R. Mann Library at Cornell University Library has pilot-tested three methods of formative and summative assessment for its library instruction program--attitudinal, outcomes-based, and gap-measure--and determined not only key areas of improvement for the program, but also the benefits and drawbacks of each method of assessment. Attitudinal assessment has guided program improvement in areas of marketing and user satisfaction but does not provide the measurement of learning that outcomes-based assessment covers. The latter can be difficult to achieve in single-session, short-term instruction, while gap-measure assessment can provide a more nuanced view of both patron and instructor attitudes toward learning outcomes, if not actual data on achievement of the objectives themselves. The authors have determined that a combination of these three different types of assessment can address the shortcomings of a single method alone and provide a better measure of the program as a whole. (Contains 10 figures.)