The 'paperback revolution' among many other effects provided the principal means of diffusion of academic knowledge to mass audiences, not as is sometimes thought in the 1960s but as early as the 1930s in the UK and the 1940s in the US. Mass-market paperback publishers Penguin in the UK and New American Library in the US commissioned original work and reprinted many classic works to very large audiences through their Pelican and Mentor lines before the better-known 'quality' paperbacks. Important works of social science, history, religion, philosophy and the history of science reached their widest audience in this form, especially in the US through unorthodox outlets such as newsstands and variety stores. The mass-market publishers combined entrepeneurial, educational and democratic methods and motivations in ways that encouraged readers to make their own choices and then fed those choices back into new commissions, repackagings and reprintings, thus acting out the 'co-production' of knowledge that is much talked about but hard to document.