The design of ship hulls girders for strength is presented in this chapter. Engineering design is introduced and the tasks of ship structural design discussed. The stages of ship structural design are presented: concept design, preliminary structural design and detail structural design. The concepts of design principles, design criteria and design philosophy are discussed and elucidated. The elastic and plastic design philosophies of ship structures are presented and differentiated. The means to perform rational design of ship structures are listed. The need to perform limit state design of ship structures is discussed and the limit states included in IACS rules mentioned. (serviceability limit state, the ultimate limit state, the fatigue limit state and the accidental limit state). The interaction of limit states is discussed as is that of relevant failure modes. In the last part of the chapter the theoretical basis of the design loads used in the IACS Common Structural Rules is described. The concept of the design sea state is introduced, the use of short-term analysis, the selection of dominant short-term sea states and the identification of dominant load components described. The concept of the equivalent design wave is introduced and in the last section design loads discussed.