There's a free draft version from the Library of Congress: https://www.loc.gov/standards/datetime/iso-tc154-wg5_n0038_iso_wd_8601-1_2016-02-16.pdf https://www.

There's a free draft version from the Library of Congress: https://www.loc.gov/standards/datetime/iso-tc154-wg5_n0038_iso_wd_8601-1_2016-02-16.pdf https://www.loc.gov/standards/datetime/iso-tc154-wg5_n0038_i... https://www.loc.gov/standards/datetime/iso-tc154-wg5_n0039_iso_wd_8601-2_2016-02-16.pdf https://www.loc.gov/standards/datetime/iso-tc154-wg5_n0039_i... Do take note of the caveats on the cover. (Not suggesting that relying on the free draft is great, just providing a reference for people interested in the actual content of ISO 8601, rather than the principles around this issue. The spec is a good read for people interested in datetime representations.)