Peer review, the process by which research output is subjected to scrutiny and critical assessment by experts before publication, has long been considered a key component of scholarly publishing. Its shortcomings have been highlighted before, but now there are increasing concerns that peer review is in crisis, some going so far as to say it is ‘broken’. There is also growing unrest amongst researchers with the traditional peer-review model. At one extreme, some critics are even proposing that everything be published, irrespective of quality. But with this model, how would non-specialists and the public know what to believe and what to treat with skepticism, what is evidence based and what is just opinion? There are calls for greater transparency and openness to be brought to a process that has been largely secret and anonymous since it was introduced three and a half centuries ago. The research publishing landscape is changing rapidly, and peer review has to evolve alongside to remain a valued mechanism of quality control. The internet has opened up great opportunities and new players are entering the arena. New innovative models are being developed, some very successfully, and journals and publishers need to adapt to survive. Whatever the model used, it is without doubt that peer review is facing considerable challenges as the range and volume of research output increases.