The flag of Luxembourg consists of three horizontal stripes, red, white and blue, and can be in 1:2 or 3:5 ratio. It was first used between 1845 and 1848 and officially adopted on June 23, 1972. Luxembourg had no flag until 1830 when patriots were urged to display the national colours. The flag was defined as a horizontal tricolour of red, white, and blue in 1848, but it was not officially adopted until 1972. The tricolour flag is almost identical to that of the Netherlands, except that it is longer and its blue stripe is a lighter shade. The red, white, and blue colouring were derived from the Grand Duke's coat of arms, which dates from the 13th century.
The colours of the Flag of Luxembourg were first adopted around 1830 during the Belgian Revolution. They were probably derived from the counts, dukes and later grand-dukes of Luxembourg's coat of arms which in turn was derived from the combination of the dukes of Limbourg's Lion and the supposed striped banner of the early counts of Luxembourg. The three-coloured horizontal design was fixed on June 12, 1845.
It took until June 23, 1972, before a law was passed regulating the flag of Luxembourg. The same law also prescribed ensign and roundel for aircraft and ships registered in Luxembourg.
One important clarification brought by this law was that the colour blue was defined as being a very bright blue, in contrast to the flag of the Netherlands (exactly the same design, but the Dutch flag uses dark blue and a less oblong shape).
The heraldic blazon for the flag is per fess Gules and Azure, a fess Argent.