An increasing interest has recently emerged in Britain in the organisation, character and development of planning systems within the 'Celtic periphery' (MacDonald and Thomas, 1997). This interest has been promoted by the Government's programme of devolution and a consideration of the implications of devolution for the operation of planning systems (Lloyd and Illsley, 1999; McEldowney, 1999; Tewdwr-Jones, 1999; Thomas, 1999). The planning system in Wales forms part of this review and continues to face a series of considerable challenges and opportunities that emerged during the 1990s (Tewdwr-Jones, 1997b). There are few detailed accounts of the development of the contemporary planning system in Wales and there exist even fewer accounts that assess in detail the various policy and advice instruments that have developed as part of that system. This account is concerned with one of the most recent planning instruments to be introduced as part of the planning system in Wales, Technical Advice Notes (Wales) (TAN[W]s or TANs). TANs were introduced in 1996 to accompany the revised format for the publication of planning policy in Wales in a single document. Planning Guidance (Wales): Planning Policy. The formal relationship between the TAN series and the unified policy document is described as one in which the policy document ?is supplemented by a series of Technical Advice Notes' (Welsh Office, 1999a, para. 1.1). The focus of this paper is to explore in further detail and in practical terms the role and function of the TAN series. Following a brief introduction to the legislative and administrative context for planning in Wales, an account is provided of the development of the modern British planning policy framework and the evolution during the 1990s of a separate policy framework for Wales. This account identifies the fragmentation of the unified policy framework for England and Wales, resulting ultimately in the system of Planning Policy Guidance Notes (PPGs) being replaced in Wales by a singular policy document supplemented by a series of TANs. The paper proceeds to define the terms ?policy' and ?advice' in order to assess the TAN series by an analysis of the function and content of the series.The legislative and administrative context for planning in Wales1One of the consequences of the wider programme of devolution and its effect on planning systems is that the singular reference to ?the British planning system' is becoming a less precise and valid term. It may be successfully argued that the term has always been ill-defined and used more out of convenience than as a proper description. The term has often been used in a practical sense to refer to the planning system as it has operated across England and Wales and testifies to the joint development of the planning system in the two countries. England and Wales have, for almost the entire history of the modern planning system, shared a common legislative, administrative and policy framework. Of these three elements, it is now only the legislative basis for the operation of the planning system that remains substantially intact and shared between England and Wales.2The administrative context for planning in Wales has been dramatically reshaped during the past five years. The first notable change in the context for planning was the establishment of unitary local government in 1996 to replace the former two-tier administrative system of counties and districts (Harris and Tewdwr-Jones, 1995). The introduction of a pattern of unitary local government is considered to have seriously undermined the capacity for strategic planning in the various sub-regions of Wales (Tewdwr-Jones, 1998). Dissatisfaction has also been expressed with the efficacy of the voluntary jointworking arrangements which are encouraged by current policy to address strategic issues (Welsh Office, 1999a, para. 3.7). The second fundamental change in the administrative context for planning has been the creation of the National Assembly for Wales. …