This e-book was developed by the Integrated MultiSector, Multiscale Modeling (IM3) project, supported by the U.S. Department of Energy, Office of Science, as part of research in the MultiSector Dynamics, Earth and Environmental System Modeling Program. It is living guide to sensitivity analysis and diagnostic model evaluation techniques for confronting the computational and conceptual challenges of multi-model, transdisciplinary workflows. Topics covered include an overview of diagnostic modeling and perspectives on model evaluation, a framework for the basic methods and concepts used in sensitivity analysis, and technical applications supporting diagnostic model evaluation and exploration.