Thousands of revellers have descended on the town of Pamplona, Spain, to celebrate the Festival of San Fermín.
The festival is famous for its 'running of the bulls' which sees thousands of visitors from around the world test their speed and nerve as they are chased around the town's narrow streets by 12 bulls.
Today's opening was traditionally marked by the launch of a rocket called a 'chupinazo' from the balcony of the city hall as crowds celebrated below, showering each other with wine and water.
The festival lasts for a week with the bull running happening each morning. Critics highlight the dangers to both bulls and runners.
Every year between 200 and 300 people are injured and there have been 15 fatalities since 1924, the last being a young Spanish man who was gored to death in 2009.
Abi Izzard, special projects coordinator for PETA UK, and Huffington Post blogger has described how the exhausted bulls are led into an arena at the end of each run to entertain spectators in a bull fight which, ultimately, ends in their death.