Peer review is an established process supporting decisions made on journal publications, grant applications, and tenure, but also helping to assess research groups. For several reasons, peer review is currently being debated, and bibliometrics could serve as its substitute. A large number of studies comparing both approaches has been published, with an overview of their results presented and discussed in this chapter. Although there are good reasons to be hesitant about utilizing bibliometric approaches to assess single persons (e. g. for tenure), the situation is different when assessing research groups. In the STM area, bibliometric indicators could be used as a replacement for peer review.