Coming up against forbidding paywalls when undertaking research or literature surveys is a common experience. Yet an increasing amount of content is available open access (OA) if you know where to look and especially if the requirements of your search are not absolutely predetermined. OAPEN‘s huge library of open access titles can be navigated via subject, language, publisher and collection. Politics, history and linguistics are the top three subjects represented amongst many others. OA-led publishers and almost all of the established major publishers will have some limited content here.
Linked site Directory of Open Access Books (DOAB) has a simpler interface and drawing on similar data is maybe easier to benchmark for a basic search for one title. For STEM subjects ScienceOpen is a researcher-facing discovery environment taking in books and journals with its USP the ability for researchers to curate their own collections and notifications of new publications. Many academic titles are also held at the Internet Archive which also includes trade books, audio and video.
Unpaywall is an open database (with browser extension) flagging up open access content in form of journal articles but it also has a very useful set of links to the open access field more widely, for example, the OA filter in the WorldCat Discovery website which can scan a list of important OA collections across all fields such as JSTOR books, Knowledge Unlatched (note also their Open Research Library) and OpenEdition Books that are worth checking out in their own right.
Larger publishers are becoming increasingly enthusiastic about highlighting their open books content with bespoke website spaces of many acting as a portal to OA book content. These include for example Routledge, Palgrave and Manchester University Press. New UK university presses such as University of Westminster Press, UCL Press and White Rose University Press have always just published their books open access. Open Book Publishers, Open Humanities Press, Language Science Press (linguistics) and Mattering Press (science, technology and society) are examples of Scholar-Led Presses with active OA books programmes with strong subject specialisms.
It is also worth flagging up some lower profile subject specific OA book portals or publishers. Perhaps your subject has one? EconStor has a limited selection of economics books plus numerous journal articles. E-International Relations is a publisher – its introductory IR textbook has been downloaded nearly 200,000 times.
Lastly the University of Westminster Library offers has a fuller list of sources of OA book titles within its Open Access Resource Guides also flagging up the Haithi Trust, OA books on Biblioboard and the US-based Open Textbook Library. It has a particularly strong section on Art Books, one of the most restricted (in terms of open access) of any humanities discipline.
In the long run there will be more visibly curated open access book collections. In the meantime a bigger challenge might be on how to fund your own open access book. A useful overview, on funding options for OA books can be found on the Radical OA website. In the meantime monographs and other titles are already a little more open for viewing than you would think.