OA publishing is compatible with peer review and we insist on rigorous, objective peer review in all our journals. We use the same procedures, standards, and select our reviewers from the same sources as are used in conventional journals. As is the case with the authors, the reviewers donate their labour, but there are considerable costs involved in organising peer review. The costs involved are largely in the time and information technology required to distribute files, monitor progress and enforce deadlines, collating and distributing comments, facilitating communication and organising versions of manuscripts.