This article discusses David Lowenthal's last book, Quest for the Unity of Knowledge, which was published posthumously by Routledge in 2019 (available in print from November 2018). The book is based on a series of lectures that he gave while a visiting fellow with the KTH Royal Institute of Technology’s Environmental Humanities Laboratory in Stockholm in 2012. Aimed at a general academic audience, it is an erudite and passionate overview showing how ingrained bias towards unity or diversity shapes major issues in education, religion, genetics, race relations, heritage governance, and environmental policy. Quest for the Unity of Knowledge explores the Two Cultures debate, initiated by C.P. Snow, concerning the gulf between the sciences and the humanities. It covers areas such as conservation, ecology, history of ideas, museology, landscape, and heritage studies, aligning with Lowenthal's career-long research interests, and serving as well as a meta-comment to the emerging Environmental Humanities.