St. Patrick's Day is now celebrated largely as a secular holiday in the United States, Canada and Australia, and has been observed in Singapore, Russia and Japan. However, its origins are steeped in Irish Catholic tradition.

March 17 is the feast day of St. Patrick, who lived in the fifth century, AD. The feast falls during the Christian period of Lent. Although Catholics often avoid eating meat during Lent, St. Patrick's Day celebrants historically have eased the restriction for the feast day. After attending church in the morning, families would feast on traditional Irish bacon and cabbage.

Until the 1970s, pubs in Ireland were closed on St. Patrick's Day in deference to the holiday's religious nature. However, celebrations have become more secular over time and in recent years, the Irish government has worked to use St. Patrick's Day as an event to increase tourism and showcase Ireland internationally. Dublin's multi-day festivities include concerts, fireworks, theater and parades.

St. Patrick's Day parades were first held in the United States (not Ireland!) and have served a variety of purposes over time. At the first parade, held in 1762, a group of Irish soldiers serving in the English army marched through New York City. In the following decades, "Irish Aid" societies held annual parades with bagpipes and drums.

Following the Irish Potato Famine that began in 1845, nearly a million Irish Catholics moved to the United States. These immigrants, who tended to be poor and uneducated, were subject to intense racism and religious discrimination. Newspapers portrayed the annual parades as drunken, violent events. As Irish-Americans became a well-organized voting bloc though, the parades became an important political event and show of Irish-American influence.