Workers, activists and rights groups have taken to the streets across the world to mark the annual holiday.
Thousands are taking to the street the world over to mark International Labour Day to protest for their rights.
While in some countries, May Day is a public holiday, elsewhere it's used to commemorate workers or protest for their rights.
This is how it is being observed over the world:
Labour unions and immigrant advocacy groups led May Day rallies in cities across the United States on Monday to protest the immigration policies of President Donald Trump.
"To me, it's offensive the policies this president is trying to implement," said Jaime Contreras, vice president of the Service Employees International Union's 32BJ affiliate, which represents cleaners and other property service workers in 11 states.
May Day, also known as International Workers' Day, has typically been a quieter affair in the United States than in Europe, where it is a public holiday in many countries.
Two officers were hurt in clashes between riot police and masked youths during a May 1 march in Paris on Monday that carried extra significance six days before the presidential election run-off.
"Masked individuals threw objects and Molotov cocktails at police" who responded by firing tear gas "and two riot police officers were injured", authorities said.
Greek trade unions marked May Day on Monday with a 24-hour nationwide strike and protests against looming new cuts demanded by the country's creditors in return for bailout cash.
Some 10,000 people demonstrated in Athens while another 3,500 marched in Thessaloniki, police said.
The strike, on a public holiday in Greece, saw businesses shuttered, ferries and trains suspended, and a state services shutdown.
South Africa's Cosatu labour federation cancelled speeches at a May Day rally including an expected address by President Jacob Zuma after the crowd became rowdy and some members booed Zuma, eNCA TV reported on Monday.
Zuma and his entourage could be seen on live TV hastily leaving the podium and being whisked in a large motorcade from the event in the central city of Bloemfontein.
Cosatu, a key political ally of the ruling ANC, last month called on Zuma to step down after his change of finance ministers triggered a credit rating downgrade to "junk".
The Cuban government's traditional May Day parade Monday is the last to be overseen by President Raul Castro – and the first without his late brother and revolutionary predecessor Fidel.
The May 1 rally draws hundreds of thousands of Cubans into Havana's Revolution Square in a sea of red, white and blue national flags and portraits of Fidel Castro.
Raul Castro has been cautiously opening up Cuba's state-run economy and strengthening its foreign relations – notably by re-establishing diplomatic ties with the United States.
But Monday's parade has the feel of the end of an era. It is not clear who will take Castro's place next year.