Harper Forum Books /
Harper Religious Department Books
A brief piece in Publishers Weekly (Going After the College Market, Feb. 27, 1967, at 40) noted that there was a growing market in the mid-1960s for "serious religious books." Harper & Row is specified as one of the publishers that "has increased the number of outlets that its religious book department salesmen call on," including college students and professors. The result of their first formalized effort to sell to the serious religious reader was the Harper Forum Books series, with Martin E. Marty as its general editor. Advertisements for the first 4 titles in the series (Science and Religion, The Theologian at Work, Contemporary Religious Thinkers, and Social Ethics) began appearing in PW early in 1968 (Jan. 22, 1968, at 71; Feb. 19, 1968, at ) with an on-sale date of March 1968.
Three more Harper Forum Books (On Being Responsible, Religious Issues in American History, and Old Testament Issues) were published in August 1968. The PW Weekly Record entry for the first two of these titles included a series number for each, RD 5 and RD 6. The Fall 1968 titles appear to be the first to have such a series number. It's clear that a decision was made, probably early on during Forum Books years, to give other religious trade paperbacks an RD series number but reserve spots at the beginning of the RD sequence for additional Harper Forum Books; hence, RD 15 was published in fall 1974, 3 years after the most recent Harper Forum Books, RD 13 and RD 14 in 1971. RD 16, Religion and Political Society, was advertised in early 1974 in PW as being for sale in June 1974, but it appears to have been published instead as RD 87, but still labeled as a Harper Forum Book, in November 1975. It seems that after the release of RD 15 in June 1974 the Harper Forum Books were published in publication sequence with the other RD books.
Much like the Harper Trade Department Books, this series is a little different from most others of the time, as they weren't necessarily unified by a common theme, besides religion, nor marketed in any particular way after the Forum Books label was dropped. The name itself is more or less a personal creation, as the only indicator that the titles belong together in a series is the use of a series number beginning with RD. That RD stands for Religious Department is simply an educated guess based on presumptions I made from references to Harper's Religious Department in Publishers Weekly and knowledge of the company's departmental organization. It seems that religious titles were given an RD series number in paperback when they didn't fall into one of the more discrete series like Torchbooks, Colophon Books, or the Perennial Library.
Note that an advertisement in Publishers Weekly (July 14, 1975, at ) has photos of the covers of the first 11 Jubilee Books, about half of which have RD numbers on them. It's clear that by the time Jubilee Books launched as a separate series in August 1975 the RD numbers had been dropped. The titles in the ad with RD numbers fall within an 11 number range of RD numbers (RD 114 to RD 124), so it seems like Jubilee Books were originally intended to be a sub-series (much like the later Forum Books) within the RD series.
There are a few sub-series, including the Harper's Ministers Paperback Library (scattered) and the Harper Library of Spiritual Wisdom, of which there are 5 titles from RD 400 to RD 404 (all 1980). The sub-series continued as a sub-series of Colophon Books (scattered) from 1981-1982.
Going After the College Market, PW, Feb. 27, 1967, at 40
Series description from volumes in the Forum Books series:
"Often dismissed with a shrug or accepted with thoughtless piety in the past, religion today belongs in the forum of study and discussion. Scholars are exploring the claims of theology, the religious roots of culture, and the relation between beliefs and the various areas or disciplines in life. Students have not until now had a series of books which could serve as reliable resources for class or private study in a time when inquiry into religion is undertaken with new freedom and a sense of urgency. Harper Forum Books are intended for these purposes. Eminent scholars have selected and introduced the readings. Respectful of the spirit of religion as they are, they do not shun controversy. With these books a new generation can confront religion through exposure to significant minds in theology and related humanistic fields.” -- Martin E. Marty, GENERAL EDITOR
Ad, PW, Jan. 22, 1968, at 71 (listing first 4 titles in Harper Forum Books).
Ad, PW, Feb. 19, 1968, at  (listing first 4 titles in Harper Forum Books).
PW, Feb. 19, 1968, at 82:
HARPER FORUM BOOKS is the title of a new religious paperback series under the general editorship of Martin E. Marty. These are sourcebooks designed for the college and church study group market.
Ad, PW, Sept. 23, 1968, at  (listing next 3 titles in Harper Forum Books).