NTP Documentation

4.2.8-series: CURRENT RELEASE: applicable to NTP version 4.2.8 through 4.2.8p18.
4.2.6-series: applicable to NTP version 4.2.6 through 4.2.6p5.
4.2.4-series: applicable to NTP version 4.2.4 through 4.2.4p8.
4.2.2-series: applicable to NTP version 4.2.2 through 4.2.2p4.
4.2.0
4.1.2
4.1.1
4.1.0
3-5.93e

NTP Security Notices and Security Policy
NTP Bug Tracker
NTP Contacts
Reference Library: Whitepapers, RFCs, and other technical documents written by Professor David L. Mills, inventor of NTP.
IETF Drafts: Proposed additions to IETF’s NTP specification.
Public Time Server Lists: Listings of public primary and secondary time servers.
NTP mailing lists
NTP FAQ:(Mostly historical) Frequently Asked Questions