The challenges of hydrogen and metals.

The Royal Society Scientific Discussion Meeting 'The challenges of hydrogen and metals' was held in Carlton House Terrace, London, UK, on 16-18 January 2017. This is the introductory article to the discussion meeting issue which includes contributed papers and seven discussion papers. Here, we introduce the motivation to hold the Meeting and give a brief overview of the contents. We conclude with acknowledgements.This article is part of the themed issue 'The challenges of hydrogen and metals'.