Open access refers to research articles that are available online for anyone to read without subscription or payment. There are three main routes to open access: green open access involves self-archiving the article in an open repository after publication; gold open access publishes the article in an open access journal and the author pays an article processing charge; and hybrid open access publishes in a traditional journal but makes individual articles open access through payment of a fee. The UK Research Councils' 2012 policy requires research funded by them to be published in open access journals or self-archived within six months of publication. Funding of article processing charges will transition to block grants to universities from 2013.