This year, the customary spring ritual falls on Tuesday, May 1, 2018.
Modern May Day celebrations have evolved into a hodgepodge of traditions including parties, sing-alongs, Old World maypole dancing, parades and workers' demonstrations, along with general protests on the streets of major capitals worldwide.
And just for a little contrast, in Hawaii it's ... Lei Day.
Historians generally agree that May Day celebrations probably originated in the spring fertility rites of ancient Rome, which occurred at about the same time of year marking celebrations honoring the goddess of spring, Flora.
By the Middle Ages, the day was being celebrated with a procession led by a "Queen of the May" chosen from a population of pretty teen girls, followed by the townspeople dancing around a maypole decorated with streamers and colorful spring flowers.
Pilgrims later brought May Day to America, but Puritans cut down neighborhood maypoles and were quick to condemn the tradition as "that Stinking Idol reviving feasts of ye Roman goddess Flora or ye beastly practices of ye mad Bacchanalians". (They also cancelled Christmas.)
May Day protests
By the late 19th century, warmer spring weather saw workers take to the streets as May Day was reborn in America as a socialist movement celebrating workers' rights and collective bargaining power.
Today - most notably in Union Square in New York City - hundreds still gather each year to protest the ever-widening pay gap between business leaders and workers.
May Day demonstrations are also prominent throughout the capital cities of Europe, where worker's rights have long been championed by a variety of socialist movements.
In its newest reincarnation on the Internet, May Day has also given Anonymous global notoriety for a series of May Day denial-of-service attacks against government and corporate sites.
More information about May Day around the Web:
Day - How it all started, including typical May Day
events & celebrations worldwide with related photos and
resoures, from Wikipedia.