The Guideline on clinical evaluation of vaccines (EMEA/CHMP/VWP/164653/2005) was developed during 2005-2006 and came into operation in 2007. It covers the design of clinical development programmes for new vaccines that are intended to provide pre- and post-exposure prophylaxis against infectious diseases. Some of the guidance provided is also relevant to the further development of licensed vaccines (i.e. generation of clinical data to support changes to the prescribing information in the post-authorisation period). Much of what this guideline says is still fully relevant to current vaccine clinical development but a revision is proposed to address issues that have come to light since it came into operation.