Performance design has been introduced h the designs for many kinds of civil structures. This technical note presents a basic framework of the performance design of coastal structures against storm surges. The performance design for the coastal structures to prevent and to mitigate coastal disasters should be developed for local citizens to clearly understand disaster prevention function of their neighbor coastal structures.
　The performance design of coastal defenses considered in this paper is based on a performance matrix, which consists of design levels and performance levels with different importance of the facility, i.e., three design levels are introduced to evaluate the performance on structural stability and disaster prevention function for the structures of three levels of importance.
　The procedure to determine the design levels is illustrated using the examples in Suoh-Nada Bay and Ise-wan Bay considering the probabilistic characteristics of the observed maximum tidal levels. Also the relation between the attacking typhoons and resultant storm surge is demonstrated using the calculations for the two bays. The procedures to determine the deformation of the structures and disaster prevention function (wave-overtopping/inundations) are also investigated. Finally, the studies necessary to employ the performance design as a standard design of storm surge defense are discussed.