This chapter discusses only structures having linear force–displacement relations. It develops the procedures to find the flexibility and stiffness of structures. The relation can be written either in terms of flexibility or stiffness coefficients. These coefficients are in fact the characteristics of the given structure and its coordinate system. The chapter also discusses the procedures for finding these coefficients for different types of structures. Similar to the flexibility method of analysis, in the stiffness method, it is necessary to have a primary structure for the analysis of structure. In the case of the flexibility method, the primary structure is a statically determinate and stable structure. Since there is no interaction between the axial and flexural deformations, the flexibility and stiffness matrices are developed using the superposition principle. An unstable structure cannot resist any load. Hence, for an unstable structure, even though the stiffness matrix can be developed, flexibility matrix does not exist.