Sharing data is good. But sharing your own data? That can get complicated. As two research communities who held meetings on this question in Rome and in Toronto in May report their proposals to promote data sharing in biology, a special issue of Nature (10 September 2009) examines the cultural and technical hurdles that can get in the way of good intentions. Some of the authors of these proposals are participating in two online forums (Rome and Toronto) at Nature Network – so please accept our invitation to visit and have your say on these questions.