ICCVAM initiated a series of “Communities of Practice” webinars in 2015 to provide opportunities for detailed consideration of a current topic relevant to alternative test method development. The first, presented on Jan. 27, 2015, was titled “Reverse Toxicokinetics: Using In Vitro Data to Estimate Exposures That Could Be Associated With Adverse Effects In Vivo.” The webinar, which attracted over 250 viewers, focused on the development and application of reverse toxicokinetic models for extrapolation of high throughput screening data to in vivo dosimetry. Presenters provided an overview of the development of reverse toxicokinetic models and discussed the consideration of population variability and sensitive subpopulations when using these models. NICEATM and EPA’s National Center for Computational Toxicology hosted the webinar on behalf of ICCVAM. Interest in the webinar prompted organization of a subsequent webinar series and workshop.