Clean Monday (Greek: Καθαρή Δευτέρα), also known as Ash Monday or (in Cyprus only) Green Monday, is the first day of the Eastern Orthodox Christian Great Lent. It is a moveable feast that occurs in the beginning of 7th week before Easter Sunday.

The day is a national holiday in Greece and Cyprus, where it is celebrated with outdoors excursions, seafood consumption, and the widespread custom of flying kites. Traditionally, it is considered to mark the beginning of the spring season.

In the year 2006, it will occur on March 6th.