This article aims to introduce a special issue on "Scientometrics of peer review", which collects papers originally presented at workshops and conferences organised by the COST ACTION TD1306 "New frontiers of peer review". Peer review is the cornerstone of science and is one of the underlying processes that bring about publication traces that are at the heart of bibliometric studies. Unfortunately, despite its importance, quantitative studies on peer review are still poorly developed, often due to lack of data. The issue aims to promote the establishment of peer review as an interdisciplinary field of research and stimulate further quantitative research.