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EEST, or Eastern European Summer Time, is the daylight saving time observed by many countries in Eastern Europe and the Baltic region. It is the summer-time offset for places that use Eastern European Time (EET) in winter, advancing clocks by one hour to UTC+3. When EEST is in effect, local time is three hours ahead of Coordinated Universal Time (UTC+3) and one hour ahead of EET (UTC+2).

Geographic usage and rules: EEST is used by countries that observe daylight saving in alignment with the European schedule. The exact dates may vary by jurisdiction, but in areas following the common European rule, daylight saving starts on the last Sunday in March and ends on the last Sunday in October. Some countries have experimented with abolishing DST or adopting year-round time, which changes whether EEST is observed.

Implementation: In time zone databases, EEST is associated with zones such as Europe/Helsinki, Europe/Tallinn, Europe/Riga, Europe/Vilnius, Europe/Kiev, and Europe/Chisinau. The term serves as the seasonal designation for the period when clocks are set to UTC+3 rather than a standalone sovereign time zone.

History and context: Daylight saving time in Europe emerged in the 20th century as part of energy-saving policies. Over time, many countries standardized on a common DST pattern, though occasional deviations and policy shifts have occurred. EEST remains the designation used for the summer offset in regions that observe Eastern European Time in winter.

See also: Eastern European Time, Time in Europe, Daylight saving time.