The official flag of Lithuania consists of a horizontal tricolor as of 2015. It is made up of three equally sized bands colored in yellow, green and red.
The current flag was decided upon at the Great Seimas of Vilnius in 1905. It was first used during Lithuania's first period of independence between the end of World War I and the country's annexation by the USSR in 1940. It was reintroduced again in 1989 and officially adopted in 1991 when the country regained its independence after the collapse of the USSR.
The three colors of the flag were chosen due to their symbolic significance to the country. The yellow color symbolizes the sun and prosperity. The green field was chosen to represent Lithuania's forests, its countryside, and liberty and hope. The red is intended to stand for the blood and bravery of those who died for the country during its multiple struggles for independence. The three colors together are meant to symbolize hope for the future and freedom from oppression.
The tricolor design of the flag is more broadly associated with republicanism, revolution and independence. The modern flags of Italy, France, Ireland and others were all introduced after the countries were first formed into independent republics during the period after the French Revolution of 1789. This type of flag was chosen in Lithuania precisely because of its association with independence and freedom from tyranny.