This chapter reflects on architectural issues arising essentially on the outside of buildings. Design issues such as integrating the programme or brief within the allowable site coverage and budget, all within an overriding architectural concept, tend to be dealt with first. For example, Viollet-le-Duc expressed the views of eighteenth-century Structural Rationalists: 'Impose on me a structural system, and I will naturally find you the forms which should result from it. The chapter considers the diversity of relationships between architectural and structural forms. It also discusses eight structural systems that exemplify synthesis between architectural and structural form. The chapter begins with shell structures, which, of all structural systems, can most closely integrate the two forms. But, it commonly encounter other examples of contrasting forms in additions or modifications to existing buildings, particularly given significant age differences between the old and new work.