The tension structures discussed in this book are predominantly roofing forms created from pre-stressed cable nets, cable trusses, and continuous membranes (fabric structures). A unique feature in their design is form-finding an interactive process of defining the shape of a structure under tension. The book discusses the role of stable minimal surfaces (minimum energy forms occurring in natural objects, such as soap films) in finding optimal shapes of membrane and cable structures. The discussion of form-finding is extended to structural forms whose shape is supposedly known, such as suspension bridge cables. .