What the tz database is and why one text file runs the world's clocks

Every computer operating system, smartphone, database server, and international airline booking system on Earth relies on the IANA Time Zone Database (often known as tzdb, tzdata, or the Olson database).

Despite coordinating billions of daily transactions, the database is not run by a multinational corporation or international regulatory treaty. It is a set of plain-text source files published directly into the public domain and maintained by volunteer computer scientists and historians.

The Theory Behind tzdb

As documented in theory.html within the source distribution, the project was founded in the 1980s by Arthur David Olson, with longtime maintainer Paul Eggert serving as principal editor since the 1990s.

The database organizes geographic timekeeping around the concept of a Zone: a geographic region that has shared uniform civil timekeeping rules since 1970. Each zone is assigned a canonical identifier in Area/Location format, such as America/New_York or Europe/London.

Why 1970?

A foundational rule of the project is the 1970 rule:

“The tz database prioritizes accuracy for timestamps after January 1, 1970 (the Unix epoch). Earlier records are maintained on a best-effort historical basis.”

Timestamps preceding 1970 often rely on conflicting historical newspapers, municipal statutes, and railroad schedules. By focusing precision on 1970 onwards, tzdb ensures that modern computer systems can convert historical UTC timestamps to local wall-clock times with mathematical certainty.

Public Domain Licensing

Unlike many software standards protected by copyright or patent encumbrances, the core data and code of tzdb are explicitly dedicated to the public domain:

Unless specified below, all files in the tz code and data (including
this LICENSE file) are in the public domain.

This dedication ensures that developers worldwide can build open source libraries, commercial operating systems, and public analytics platforms without licensing restrictions.

Explore the complete collection of tzdb releases or learn about our data methodology.