Peroni, Silvio. The Open Citations Movement : The Story So Far. 
The 5th Conference on Scholarly Publishing in the
Context of Open Science – PUBMET 2018
20-21 September 2018, Zadar, Croatia, 20/09/2018. https://figshare.com/articles/The_Open_Citations_Movement_the_Story_So_Far/7110653

The Initiative for Open Citations (I4OC) was launched in April 2017 with the purpose of promoting the release of structured, separable, and open citation data. Thanks to the incredible support of a large (and still growing) number of publishers and stakeholders, in one year more than 500 million citations have been released to the public, and are currently used by third parties for building new services to serve the scholarly community.

Source :
https://figshare.com/articles/The_Open_Citations_Movement_the_Story_So_Far/7110653