In the flow of information all around us – in businesses, governments, personal spaces, in the physical and online world, there is information that we want to fix at a point in time and give it an identifier that we know we can use to find it again. That is, be kept in a way so that it remains not only identifiable with a meaningful name, but also so it is inviolate and trustworthy over time. The information might be born digital (emails, datasets, web pages, tweets, PDF documents), digitised copies of physical formats (books, paper documents) or still in physical form only.