The Indigo Book

Founded by New York University professor Christopher Jon Sprigman, authored collectively by Sprigman and a group of NYU law students, and published by Public.Resource.Org, it is an adaptation based on the 10th edition of the Bluebook as published by the Harvard Law Review Association in 1958, which had entered the public domain in the United States because its copyright had expired due to non-renewal.

The project was inspired by correspondence between Public.Resource.Org's founder Carl Malamud and a Nagoya University academic, who was threatened by lawyers representing the HLRA over plans to incorporate the Bluebook system into the open source citation management program Zotero.

[3] Research conducted by Malamud and Sprigman found that the 10th edition of the Bluebook, published in 1958, had fallen into the public domain because its copyright had not been renewed, as required by U.S. law at the time.

On October 6, 2014, Sprigman sent a letter of response to the Harvard Law Review Association, disclosing these findings and arguing that the content of the then-current 19th edition was nearly identical to the 10th barring trivial changes.

"[3] In December 2015, following Twitter postings by Malamud teasing the upcoming release of Baby Blue, the Harvard Law Review Association threatened legal action against the project, as it believed that the name Baby Blue had a confusing similarity to the "Bluebook" trademark, and requested a copy of the publication to perform intellectual property examinations under a presumption that it may be substantially similar to the copyrighted work.