The Drug Matrix is concerned with the treatment of problems related to the use of illegal drugs by adults (a similar table deals with alcohol-related problems). It maps the terrain within which relevant evidence may be found and for each location tries to find the most important UK-relevant research and guidance. In widening contextual circles, across the top of the matrix the columns move from specific interventions through how their impacts are affected by staff, the management of the service, and the nature of the organisation, to the impact of whole local area treatment systems. Down the rows are the major intervention types implemented at these levels. At the intersections, inside each cell is our pick of the most important documents relevant to the impact of that intervention type at that contextual level.