Crystal Kay Williams (クリスタル・ケイ・ウィリアムズ, Kurisutaru Kei Wiriamuzu, born February 26, 1986) is a Japanese singer, songwriter, actress and radio host.

After releasing her first single, "Eternal Memories" (1999), Crystal Kay gained fame for her third studio album, Almost Seventeen (2002), which debuted at number 2 on the Japanese Oricon charts. Almost Seventeen eventually sold over 400,000 copies and was certified platinum by the Recording Industry Association of Japan. Crystal Kay, formerly signed to Epic Records, a sub-label of Sony Music Japan for 12 years, suddenly transferred to Delicious Deli Records, a sub-label of Universal Music Japan in 2011.

As of April 2021, she has released thirteen albums. Her seventh studio album, All Yours (2007) became Crystal Kay's only number-one release in her career when it debuted on top of the Oricon chart in June 2007. Throughout her career, Crystal Kay has collaborated with M-Flo and BoA, Chemistry as well as other well-known recording artists. With over 5 million records sold to date, Crystal Kay is one of the best-selling musicians in Japan.