OpenAPC collects, aggregates, and publishes data on Open Access journal articles (APCs), Open Access Books (BPCs) and other cost data from participating institutions. It aims at transparency, comparability and tracking of cost developments in the field of Open Access publishing. Therefore, OpenAPC allows libraries, funding agencies, researchers, developers and 3rd party services to keep track and provide access to the Open Access record of European expenditure for APC or other cost data, e.g. from transformative agreements, across publishers, journals, academic institutions and countries. All OpenAPC data is made freely available under the Open Database License (ODBL). OpenAPC complies with current recommendations for cost transparency in an Open Access based scholarly publication system. It is important to point, that all data is provided voluntarily by universities and other HEI, funders or national consortia. Major PlanS cOAlitionS members and supporters e.g. Wellcome Trust, FWF, or the Bill & Melinda Gates Foundation are already contributing data to OpenAPC.