In this paper we re-examine the work of Lindholm-Romantschuk (1998), who was the first to study disciplinary knowledge flows using book reviews from the social sciences and humanities. Our study is based on a current, and larger sample of book reviews and includes reviews written for scientific books as well. We use a different approach to classifying book titles, and employ different indicators for measuring knowledge INflows and OUTflows. For most book reviewing disciplines, a book is likely to receive on average one or two reviews across a five-year period. Some disciplines have books that are reviewed ≥10 times, and it is with this 'elite' sample that we develop VOSviewer knowledge flow maps, and measure Flow Ratios (FR) as well as OUT/IN Ratios (OI). Our maps show where the strongest overall knowledge flows exists amongst different disciplines. We also show the degree to which book reviewing disciplines possess permeability of boundaries. Those with a lower degree of permeability (e.g., History) tend to be highly independent. They may take in reviews, but do not 'need' other disciplines for external reviews, while those with a balanced INflow-OUTflow tend to exchange reviews a lot with other disciplines (e.g., Linguistics; Sociology; Communication studies).