Women's History Month is celebrated annually in March. It was officially designated as Women's History Month by the U.S. Congress in 1987, with celebrations centered around the week of March 8 to correspond with International Women's Day. Since then, each year in the United States, the month of March is set aside to honor the contributions and achievements of women in history and society.

To summarize:

• Women's History Month is celebrated in March.
• It originated as Women's History Week in 1978, focusing on the week surrounding March 8.
• It became a month-long national observance in 1987.
• International Women's Day, March 8, is a key focal date within the month.

Thus, Women's History Month is in March every year.