The United Procession of Women, or Mud March as it became known, was a peaceful demonstration in London on 9 February 1907 organised by the National Union of Women's Suffrage Societies (NUWSS), in which more than three thousand women marched from Hyde Park Corner to the Strand in support of women's suffrage. Women from all classes participated in what was the largest public demonstration supporting women's suffrage seen up to that date. It acquired the name "Mud March" from the day's weather, when incessant heavy rain left the marchers drenched and mud-spattered.

The proponents of women's suffrage were divided between those who favoured constitutional methods and those who supported direct action. In 1903 Emmeline Pankhurst formed the Women's Social and Political Union (WSPU). Known as the suffragettes, the WSPU held demonstrations, heckled politicians, and from 1905 saw several of its members imprisoned, gaining press attention and increased support from women. To maintain that momentum and create support for a new suffrage bill in the House of Commons, the NUWSS and other groups organised the Mud March to coincide with the opening of Parliament. The event attracted much public interest and broadly sympathetic press coverage, but when the bill was presented the following month, it was "talked out" without a vote.

While the march failed to influence the immediate parliamentary process, it had a considerable impact on public awareness and on the movement's future tactics. Large peaceful public demonstrations, never previously attempted, became standard features of the suffrage campaign; on 21 June 1908 up to half a million people attended Women's Sunday, a WSPU rally in Hyde Park. The marches showed that the fight for women's suffrage had the support of women in every stratum of society, who despite their social differences were able to unite and work together for a common cause.