The national flag of Bulgaria is a tricolour consisting of three equal-sized horizontal bands of (from top to bottom) white, green, and red.

In 866, Pope Nicholas I advised Prince Boris who had recently Christianised his people to switch from the practice of using a horse tail as a banner to adopting the Holy Cross.

On those maps, the flags commonly have a white or golden[5][6] background and depict either the insignia of the ruling House of Shishman,[7] or unknown symbols[8][9] in red.

[10]After the establishment of the People's Republic of Bulgaria in 1946, the new Dimitrov Constitution of 1947 changed the flag: the colors and their order remained the same, but the new national emblem was placed on the left side of the white stripe.

The new emblem contained a lion within a wreath of wheat ears below a red star and above a ribbon bearing the date 9.IХ.1944 (9 September 1944), the day of the coup d'état of 1944 which had ended the monarchy.

(2) The national flag of the Republic of Bulgaria is tricolour: white, green and red fields, placed horizontally from the top downwards.

On fixing the national flag in a vertical situation of the carrying body the colours shall be arranged from left to right - white, green, red.