Abstract: New cement binders characterised by including: 30-80% by weight of a first component having MgO and at least one magnesium carbonate having the general formula: w MgC03.x MgO.y Mg(OH)2.z H2O (A) in which w is a number equal to or greater than 1; at least one of x, y or z is a number greater than 0 and w, x, y and z may be (but need not be) integers and 20-70% by weight of a second component including a least one silicon and/or aluminium oxide containing material are disclosed. They can be used to produce building materials (cements, mortars, grouts and the like) having improved structural properties relative to prior art materials. In particular, their manufacture is less energy intensive than e.g. Portland cement making them environmentally friendly in the sense that processes for their manufacture have a relatively low carbon footprint.