Article Processing Charges (APCs) are charged to authors of scholarly articles during the publication process. APCs are used by open access journals in lieu of subscription fees that libraries and readers traditionally have paid to gain access to research articles. They shift the burden of journal production costs (editing, peer review, hosting, archiving, preservation) to authors. Paying an APC results in an article that is available to anyone with an internet connection. Corporate, non-profit, society, academic, and other publishers use a variety of models to meet their income needs and publishing service costs, and charging APCs is one model.
Generally the submitting author must agree to pay the publication charge minus any eligible discount (or request a waiver) at the time of submission. APCs are paid after an article is accepted for publication and before it appears in the journal. APC amounts vary by journal, and they are not charged by all open access journals, particularly in the humanities where researchers rarely have grants to cover the fees.
APCs should not be confused with page charges long associated with both print and digital publications. Page charges are used to cover administrative costs as well as the cost of print publication, but do not make the article available in an open access (OA) model. APCs are also distinct from submission fees, which are rare and should be looked on with suspicion by authors evaluating journals for quality.
Journal APCs vary greatly. Many OA journals are free to publish in, but at the higher end of the spectrum APCs can be around $3000. Check an individual journal's "information for authors" section, or review a journal's "publication charges" section in the Directory of Open Access Journals for information about APCs, submission charges, and waiver policies.
The Eigenfactor Index of Open Access Fees can help authors to engage in comparison shopping between scholarly OA journals. Be sure and check out the information page to understand data sources and methods behind this tool. The image demonstrates how to read the data: High Article Influence (AI) and lower APC cost = "good deals!".
There are many reasons to publish in a journal that charges APCs.