Despite the continual round of annual conferences, special sessions and symposia that provide ample opportunity for researchers to get together and talk about igneous processes, the origin of laccoliths and sills continue to inspire and confound geologists. In one sense this is surprising. After all, don't we know all we need to know about these rocks by now? As testified by the diverse range of topics covered in this Specical Publication and elsewhere (Breitkreuz & Petford 2004), the answer is clearly no.

This Special Publication contains 13 papers that cover a diversity of perspectives relating to the geology and emplacement of sills, dykes and laccoliths that together help advance our understanding of their formation. Ablay et al. describe a new fracture-mediated intrusion model that attempts to resolve the sequence of magma and rock displacements comprising felsic magma systems coupled with a thermal model for the lower crust, arguing that the system is driven fundamentally by partial melting at source. Thomson & Schofield report on the relationship between sills, dykes, laccoliths and pre-existing basin structure in the NW European Atlantic margin. Using three-dimensional (3D) seismic data, they interpret the sills as predominantly concave-upwards in shape with flat inner saucers connected to an outer rim by a steeply inclined sheet structure. Magma flow patterns, as revealed by opacity rendering, suggest that sills propagate upwards and outwards away from the magma feeder. Magma emplacement below the level of neutral buoyancy would allow sill inflation and country rock deformation. Fracturing of country