The system update 2013 document summarizes notable changes to CrossRef's deposit and query systems, including allowing deposits of stand-alone CrossMark and FundRef data, inclusion of MathML in article titles and abstracts, ability to query on Orcids, improved data replication, and hardware upgrades. It also provides statistics on DOI clicks and source articles for the year. Plans for the future include assigning multiple DOIs to books from different members and allowing references to non-CrossRef DOIs such as those assigned to databases.