Early origins and historical perspectives of time measurement.

Information about calendar history and calendar reform.

A categorized collection of calendar related sites.

Includes an ecclesiastical calendar and a section on old and new style dating.

Explains the differences between several time systems.

Explains the importance of concept of time in the history of mathematics, science and measurement.

Information and history about Daylight Saving Time all over the world.

An overview of the ISO 8601 notation for dates.

Time has been studied for thousands of years. Nevertheless, many issues remain to be resolved. This article explores both what is now known about time and what is controversial and unresolved.

The National Institute of Standards and Technology maintains time and frequency standards for the United States.