the impact on global ecological balances caused by the industrys massive energy consumption. When we include fuel use for mining and raw material transport, cement production takes about 6.3 gigajoules (six million Btus) for every ton of cement. This makes cement production approximately ten times as energy-intensive as the North American economy. In some Third World countries, cement production accounts for as much as two-thirds of total energy use (Wilson, 1993). This is particularly disturbing when one considers that, because of the development needs of Third World, the demand for Portland cement in the world is projected to double in the next few decades (Mehta, 1998a). Ecological solutions for concrete problems involve changes in production. But perhaps the most influential decisions are those of building designers and developers in selecting materials. They can affect what and how things are produced. There are four main strategic foci for the green building movement: first, finding alternatives to concrete; second, when its use is appropriate, designing to use less of it; third, using more ecological concrete that contains substantially less Portland cement; and lastly, finding ways to recycle C&D concrete, and designing concrete materials for reuse. In this brief overview, I can only touch on key examples of each focus. The principal means of replacing concrete is clearly the use of steel. Life cycle comparisons of steel and concrete over the last decade have indicated that steel may be the more appropriate choice for many structural applications. Germanys Wuppertal Institute compared the use of steel and concrete for pylons, bridges and similar structures in the OECD countries. Using the MIPS conceptmaterial input per service functionit found that a threefold improvement in material efficiency could be gained