  Open Access (OA) books available through the Directory of Open Access Books
(DOAB) are investigated and the number of titles, the distribution of subjects,
languages, publishers, publication years, licensing patterns, etc., are
clarified. Their chronological changes are also shown. The sample comprised
10,866 OA books, which were available through the DOAB as of February 24, 2018.
The results show that OA books are increasing in number at an accelerating
rate. As for distribution of subjects, Social Sciences ("H" in the Library of
Congress Classification [LCC] codes), Science ("Q" in LCC) and World History
and History of Europe, Asia, Africa, Australia, New Zealand, etc. ("D" in LCC)
are the most popular. As for languages, English, French, and German are the
most popular. As for publishers, Frontiers Media SA, Presses universitaires de
Rennes, and ANU Press are the most popular. Many books are newly published
ones, but older books, published in or before 1999, also began to be available
recently. As for the licensing patterns, "CC by-nc-nd" and "CC by" are the most
popular. Considering these tendencies, libraries should begin to utilize OA
books.
