Rainbow is the fifth studio album by Ayumi Hamasaki. It was released on December 18, 2002, by Avex Trax, less than a year after her previous studio effort I am.... The album sold about 445,000 copies on the first day of its release, and also became number one on the Oricon Daily Charts and also topped the weekly charts. The album was one of the successful albums of the month, topping the Monthly Charts and also reached number two on the yearly charts.

Three singles were released to promote the album - all of which became number one singles on the Oricon weekly charts. The lead single, "Free & Easy" started a streak on number one debuts for Ayumi Hamasaki, which continues till date. The second single "H" - an EP became Hamasaki's sixth Million selling single and also made her the only artist to accomplish this feat. The third and final single "Voyage" was nominated for a Gold Disk Award.

To date Rainbow has sold over 1,858,000 copies and has been certified two times million by RIAJ and is the 89th best selling album in Japan.