On 25 July, the day of St. James, Vitoria-Gasteiz celebrates a very lively festival, traditionally known as "the day of the shirts".

The origins of the festival are relatively recent, dating back to the year 1926, in which a group of friends that were going to the bullfight had their working shirts on, to avoid getting dirty, and they jumped, in the heat of the festivities, in front of the brass band, showing their festive mood. This seemed to have left its mark among the people of Vitoria, and soon other groups of friends, or "cuadrillas" as they are known in the Basque Country, appeared dressed with working shirts, which later became the traditional dress, more folkloric: the: "txapela" (Basque beret), white shirt, baggy shirt, red or blue neckerchief (to avoid sweating around the neck of the shirt, loose trousers with a wide belt, and "abarcas" (thick leather shoes that are tied with laces to the leg).

The festival starts in the Plaza Nueva at 9 am, where the "txistularis" and the municipal band sound the waking up call. The unstained "blusa" or baggy shirt is worn for the occasion, as required by tradition.

Meanwhile, on the San Francisco sloped street there are many different stalls with strings of garlic, with around 50 heads of garlic on each. It is quite traditional to buy them and carry them around during the festival, and it is on this day when the majority of garlic is bought in the city for the whole year.

The high point of the festival is at 5 o'clock in the afternoon, when the different "cuadrillas" march, dressed in the traditional costumes, among a multitude of festivity and fun. Another special mention must be given to the fun packed donkey race, in which the representatives of the different cuadrillas compete against each other, riding a donkey.