There’s a good reason why steel is regarded as a particular challenge for designers. Barely another material exists that can offer such precision over large dimensions. Huge spans or cantilevers of 30 to 40 metres – such as those by Santiagao Calatrava in Liège, in Belgium – can be realised without problems. With his station concourse, Calatrava proves once again what a light, transparent overall effect can be achieved, despite the fact that 10,000 tonnes of steel are used. In an interview with us, Calatrava discusses his visions as an architect, engineer and sculptor. Meanwhile, with their design of a steel company’s sales centre in Linz, Austria, Dietmar Feichtinger Architectes also draw attention to the potential of steel, with a large cantilever over the entrance forming a distinctive element of the building. The array of different forms that steel can take in buildings is fascinating, as shown by our selection of examples including the perforated metal sheeting on the exterior of a small workshop in Zurich, such as those often used by Dominique Perrault (including on the tennis centre in Madrid), or the mighty, open-span profiles of a protective building at an archaeological find spot as realised by Paredes Pedrosa arquitectos in Spain. This construction is symbolic for the range of possibilities available with steel construction today, whether polished, laminated or specifically corroded. The fact that the choice of joining method for the construction elements is very much a design factor is shown by the comparison of steel joinings in the article from Alexander Reichel and Gerald Schnell. If one looks at sustainable construction not just in terms of energy and the environment, another important factor – particularly for steel buildings that tend to have a longer lifespan – is whether a building is accepted and well-used in the long term. This means that in addition to all its functional design elements, the memorable architecture of a building is also crucial.