Millions of people worldwide take part in massive anti-war protests in anticipation of the United States and its allies invading Iraq.

On 15 February 2003, there was a coordinated day of protests across the world in which people in more than 600 cities expressed opposition to the imminent Iraq War. It was part of a series of protests and political events that had begun in 2002 and continued as the war took place. Social movement researchers have described the 15 February protest as "the largest protest event in human history".

Sources vary in their estimations of the number of participants involved. According to BBC News, between six and eleven million people took part in protests in up to sixty countries over the weekend of 15 and 16 February; other estimates range from eight million to thirty million.

Some of the largest protests took place in Europe. The protest in Rome involved around three million people, and is listed in the 2004 Guinness Book of World Records as the largest anti-war rally in history. Madrid hosted the second largest rally with more than 1.5 million people protesting the invasion of Iraq; Mainland China was the only major region not to see any protests on that day, but small demonstrations, attended mainly by foreign students, were seen later.