The Japan Open is a men's tennis event hosted in Koto, Tokyo, Japan, in Ariake Tennis Forest Park, which includes the Ariake Coliseum. Because the Ariake Coliseum is being refurbished for the tennis events at the 2020 Summer Olympics, the site was changed to the Musashino Forest Sports Plaza in 2018. The event, which has been held since 1973, features men's singles and doubles competitions.

The Japan Open was a mixed event for men and women from 1979 until 2008. This is no longer the case since the Ariake Coliseum hosted the Pan Pacific Open, another women's professional event. The Japan Open was a WTA Tour tournament until 2008 when it was demoted to a $100,000+H ITF Women's Circuit event. The women's competition was stopped in 2010.

The men's competition is part of the ATP Tour 500 series. The Japan Open was known as the Tokyo Outdoor Grand Prix and was a member of the Grand Prix tennis tour from 1973 and 1989 until the men's event was reorganized with the introduction of the ATP Tour.

Japan Open 2021: Why has the Tokyo ATP 500 tournament been canceled?

Due to the coronavirus pandemic and travel restrictions, the men's and women's tennis circuits altered their end-of-season itineraries in June, excluding matches from China and Japan.

The China Open in Beijing and the Japan Open in Tokyo were been canceled, ATP and WTA confirmed earlier. The final dates of the Indian Wells tournament's comeback, from October 10 to 17, were added in the calendar update.

Due to the pandemic, Indian Wells, the ATP Masters 1000, and WTA 1000 were canceled in 2020 and rescheduled for last March, its regular month.