Irregularly shaped buildings with double curved surfaces, also known as free forms or Blobs, have regained interest from architects. Those actually built however, despite their futuristic look, have load-bearing structures which are still based on conventional principles, as building systems suitable for these new shapes do not exist. The present research aims at proposing structural systems which are appropriate for free-form building designs, that is to say, which are able to follow the architectural shape and still can be built. For this, a) fabrication techniques, b) geometrical descriptions and c) principles of load transfer have been inventoried. Built examples of free-form buildings and similar objects were studied and categorised according to the inventory. From this study, search directions have been defined. Exploration of these has resulted in 23 highly abstract structural schemes. These have been developed further into 3 structural systems. The systems resulting from the research offer unprecedented freedom to shape load-bearing structures, while they can also be rationally built. Furthest developed (including prototypes) of these proposed solutions is the Delta Ribs system. In this system, steel members called Delta Ribs are applied in a network structure in which each rib shapes itself with respect to the local geometry and the required structural capacity at that point. Load-bearing structures can now be fully and effectively integrated in free-form building shapes.