A selective layer melting or other additive layer fabrication method in which powdered material is fused by heating it with a pulsed laser, the pulses being modulated while the laser is traversing the substrate so as to control the thickness and/or width of the layer being formed. Initial layers of the fabrication structure may be formed more thickly than subsequent layers, e.g. by means of a CW laser, to reduce distortion. This aspect of the invention may be employed independently of the use of a pulsed laser to form the subsequent layers.