From the Irish capital of Dublin to the U.S. city of Chicago, people around the world are donning green Saturday and celebrating St. Patrick's Day.

The March 17 holiday commemorates the most recognizable of Ireland's patron saints and the arrival of Christianity in Ireland centuries ago.

Hundreds of thousands of people lined the streets of Dublin Saturday to watch the annual parade, one of many taking place across the country. The event featured marching bands, and theater and dance groups from around the world.

In the British town of Aldershot, Prince William's wife, Catherine, the Duchess of Cambridge, marked the occasion with her first solo military engagement. Wearing a green coat dress, she presented members of the 1st Battalion Irish Guards with sprigs of shamrock in a tradition dating back to 1901.

Irish expatriates in Hungary also got into the spirit with a parade in the capital, Budapest. Participants dressed up as leprechauns, danced and in keeping with St. Patrick's Day tradition, kept the beer flowing.

Across the Atlantic, thousands of Americans gathered to see the Chicago River dyed green. Irish Prime Minister Enda Kenny was in Chicago to take part in the city's parade. Parades were also being held in New York and other U.S. cities, while Irish bars and restaurants were serving green beer and traditional Irish food.

The U.S. is home to many with Irish roots. A large number of ancestors of Irish-Americans came to the U.S. in the 1840s to escape Ireland's great famine.