This thesis examines the use of information, particularly that of a technical kind, in decisions and policies in land use planning, and reports on empirical analysis on the making of development plan policies by local authority planning departments. The research examines the role of technical information in planning processes and starts by identifying different ideas put forward about the potential contribution of computerised systems to the provision of such information. It is concluded that the literature on decision processes in planning has a number of weaknesses in relation to how the use of information is understood. Research on the use of information in planning has found a complex picture which is at odds with many normative theories of planning. However, an empirically based theory of the use of technical information in planning, including that from computerised sources, is poorly developed. The thesis argues that the idea of a set of policy processes - structuring access, mode of debate and decision criteria in planning decisions - is a powerful analytical tool in understanding planning practice. Using this as a base, a conceptual framework relating these processes to information use is developed from the available literature and the findings from exploratory interviews. Through a set of six case studies oflocal authority planning departments the explanatory power of this framework is assessed. On the basis of this a refined framework is put forward and a final assessment made of it using a detailed analysis of the evolution and adoption of the policies in two development plans, the Wakefield Unitary Development Plan and the Lancashire Structure Plan. The research concludes that the use of technical information is heavily influenced by the regulatory nature of the British planning system, which places a focus on the justification of policies and gives greater importance to technical analysis in some situations than others. In development plan making the semi-judicial arena of the inquiry or examination in public is central. Information from computerised sources can playa distinctive role in planning but this is dependent on how it is incorporated into the policy processes through which decisions are made. Technical information and computerised analysis can play an important role in legitimating planning decision and shaping the evolution ofpolicies, but this can only be understood within a wider context of social and political processes.