Viking Portable Library
Publisher: Viking Press
Viking launched its successful Portable Library in 1943 and had released around 60 titles in cloth by the time it decided to release paperbound editions in March 1955. The first 10 paperbound editions were P11 (Whitman), P20 (Twain), P21 (Rabelais), P28 (Lawrence), P32 (Dante), P36 (Hawthorne), P39 (Greek Reader), P41 (Voltaire), P46 (Medieval Reader), & P60 (Gibbon).
The series continued past the Nov. 21, 1975, sale of Viking to Penguin in 1975, being the only Viking series to maintain its own name and identity, at least until it started bearing the Penguin logo around 1977. In total the series numbers ran up to P79 in paperback, although it still persists today in paperback, albeit in thoroughly Penguin dress, with no mention of Viking.
Viking Portable Library in Paper Covers at $1.25, PW, Dec. 18, 1954, at 2346.
Ad, PW, Jan. 15, 1955, at 174-175 (two-page spread announcing the first 10 titles in the paperbound Portables editions, "with a bow to Anchor and Vintage.")
Viking Portables Carry On, PW, Mar. 5, 1973, at 39 (celebrating the 30th anniversary of the Portables on the occasion of the publication of the 75th title in the series).
Viking and Penguin: Big U.S. Move from U.K., Worldwide PB Distribution for Americans, PW, Nov. 17, 1975, at 14, 16.
All Viking paperbacks, with the exception of Viking Portables, will in future be published under the Penguin imprint.
Penguin Books Is Taking Wing, and Looks to Become a Competitive American Bird, PW, Dec. 6, 1976, at 45.
A paperback tradition that had been available from Viking was the Viking Portable. What is to be the fate of this imprint? Mohrfeld says, "Its identity in life is certainly as the Viking Portable and it wouldn't make much sense to change that name. But, in the future, the Viking Portables will carry the Penguin logo."
For Love of Books: The Viking Portable Library, Nighthawk News, July 9, 2010, https://nighthawknews.wordpress.com/2010/07/09/for-love-of-books-the-viking-portable-library/ (blog post from a collector of Viking Portables).
How I Spent My Summer Holidays or, Fun with the Viking Portable Library, Books, Reading, and Me: A Bibliomane Blog, Sept. 20, 2017, https://bibliomaneblog.wordpress.com/2017/09/20/fun-with-the-viking-portable-library/ (thorough exploration of the various incarnations of the Viking Portables).
Viking Portable Library, A Series of Series, https://seriesofseries.owu.edu/viking-portable-library/ (high-quality scans and a listing to #75).