The DOI foundation is responsible for "making sure DOIs work" (I'm sure there's a better definition than that!). Like DNS, there are a number of Registration Ag

The DOI foundation is responsible for "making sure DOIs work" (I'm sure there's a better definition than that!). Like DNS, there are a number of Registration Agencies (RAs) who are responsible for registering DOIs. An organisation such as CrossRef (or DataCite) RA will say "we want to become an RA". They join, and can then register their own DOIs. DOIs are persistent identifiers, and the main reason you want those is so you can have a persistent link from one thing to another. A normal hyperlink is subject to link-rot, which is an especially bad problem when you've got printed journals or online 'printed journals'. A DOI is a link that goes via the DOI to redirect to wherever the link is meant to point at this point in history. RAs are responsible for registering DOIs and updating the link redirect data whenever the thing being pointed to moves. RAs exist for different purposes. CrossRef exists to enable linking between scholarly publications, so we register DOIs for scholarly publications (journal articles, books, etc). DataCite exists to enable linking to objects like datasets. CrossRef isn't just an DOI RA, but DOIs are a big part of what we do. In addition to this we store metadata from publishers and then let anyone use our APIs to get that data. The DOI foundation maintains a load of DOI resolution servers. They all do the same job: you click on a link, you're load-balanced to one of the machines, and it replies with the relevant redirect. Normally when you click on a DOI in a browser, you are redirected to the appropriate URL. We introduced 'Content Negotiation' for DOIs, which means you can supply an 'Accepts' header and get more bibliographic information about a DOI. This works with a redirect. Here's an example: curl -L -iH "Accept: text/turtle" http://dx.doi.org/10.5555/515151 http://dx.doi.org/10.5555/515151 That query is answered by one of the DOI servers. It doesn't matter which. You see you're redirected to Location: http://data.crossref.org/10.5555%2F515151 http://data.crossref.org/10.5555%2F515151 This is a CrossRef server and it knows all the publication metadata. This then serves all the bibliographic data. So TL;DR: 1 - The DOI foundation runs the DOI system 2 - CrossRef is an RA for DOIs 3 - Every RA runs its own resolution servers to spread the load 4 - Every resolution server can answer any DOI registered by any RA 5 - If you ask for bibliographic content negotiation on a CrossRef DOI, you'll be redirected to the data.crossref.org server which will give you what you asked for And that DOI that worked on dx.doi.org but not data.CrossRef.org might be because it can take a day for the data to propagate to various systems. Any questions, labs@crossref.org