The red ground symbolizes the Biscayan people (the race); the green saltire might represent the Oak of Guernica, a symbol of the old laws of Biscay, or Fueros; and over them, the white cross, God's symbol of Basque Catholic devotion. Thus, red, white and green have become the national Basque colors.
The flag was designed in 1894 to represent the province of Biscay in a set of one flag for each of the seven Basque provinces and one for the whole country; however, since PNV activity was scarce outside of Biscay, only the Biscayne flag was publicly recognized. It was hoisted for the first time in the "Euzkeldun Batzokija", the club that preceded EAJ-PNV. The party adopted it in 1895 and, in 1933, proposed it as the flag of the whole Basque Country.
In 1938, after the military defeat of the Basque Government the regime of General Franco prohibited this flag —although it continued to be used in the Basque departements of France. In the following decades it became a symbol of defiance – the first actions of the clandestine group ETA involved placing flags in public places.