NIST SP 800-38A
The US standard that first specified the five block cipher modes, published in 2001.
Published in December 2001, SP 800-38A describes ECB, CBC, CFB, OFB and CTR, with test vectors so that an implementation can be checked against known answers. For years it was the reference that libraries and protocols pointed to when they chose a mode.
The modes give confidentiality but no protection against modification. That is why the series later added CMAC in SP 800-38B (2005) and GCM in SP 800-38D (2007). NIST now steers most users towards authenticated modes, so SP 800-38A is mostly read today for its definitions and test vectors.