There have been many occasions in the past when this publication has released papers online ahead of their appearance in print. Usually these have been high-profile papers announced at a conference. In such cases, we felt it desirable or even essential to make the paper widely available as soon as possible.

In principle, the sooner a paper is published, the better for all concerned. What is more, researchers increasingly access papers central to their research via the web rather than print. So it is a natural and desirable step to make such advanced online publication a more routine process. This we have already initiated. The appearance this week of an additional printed contents page reflects our commitment to the service and an expectation that the number of papers published in this way will gradually increase. But although we recognize that competition needs to be taken into account, we will oppose the misuse of advanced online publication in that context, resisting any tendency to cut corners from the process of publication.

The point at which publication occurs should be clearly and unambiguously defined: publication occurs at the moment the paper is first made available to Nature's readers, that is, when it is posted online, which could be on any day of the week. Moreover, the online version will be fully edited, and not subject to subsequent change.

Citations of print references are of little use to researchers accessing the literature online. Thus, we will encourage people to refer to a paper's Digital Object Identifier (DOI; see http://www.doi.org) before its appearance in print and, after printing, to retain a citation to its DOI alongside the traditional print reference.

Nature papers published ahead of print can be seen at http://www.nature.com/nature/aop, from which there is a link to a full explanation of the Nature Publishing Group's Advance Online Publication service (AOP). AOP is to be used by all of the Nature research journals.