Compared to journal level metrics, sources for quantitative book level metrics are more limited. The most direct evidence of impact are citations in other scholarly publications. While not specifically research impact, one might consider the number of libraries that acquired the book, downloads if an online book, and the book's use in a curriculum at other institutions. Some might consider the latter an educational (or even societal) impact. Consider using more qualitative evidence too, such as book reviews and book awards (or nominations). Alternative metrics (altmetrics) such as citations in policy documents and patents, as well as mentions in the media may provide evidence of impact or public engagement. Consider how the book changed the field, professional practice, guidelines, or methods. Then look for evidence to support it.