The Yokohama Minato Mirai Hall was planned as a complex cultural facility on the waterfront of Yokohama City and was opened in June 1998. In this building, a large concert hall with 2020 seats (mainly for symphony concerts) and a small concert hall with 400 seats mainly for chamber music are included. For the design and construction of this building, an acoustic design and research group consisting of architects, acousticians, and building engineers was set up and such various acoustic problems as room acoustics, sound insulation between rooms and facades, prevention of structure-borne sound from subway by floating floor construction, and noise reduction of the air-conditioning system were investigated by cooperative work in the group. For the acoustic design of the two halls, computer simulation based on geometrical acoustics and a 1/10 scale model experiment were performed for checking room shape and auralization studies. During and after the construction, acoustic measurements were carried out under various conditions. Before the opening, test concerts were performed with an audience, and acoustic data under occupied conditions were obtained. In this paper, the outline of the design process and the acoustic characteristics of the two halls are introduced.