Background: In year 2004 the Stockholm County Council (CC) approved a policy to reduce overweight and obesity. The implementation at local level started in two pilot municipalities during a two years period and resulted in several subprojects. Program theory (PT) is a methodology used to understand and identify key components in complex programs.

Objectives: To highlight strategies and tools applied in planning and conducting an implementation evaluation of a CC policy in two municipalities.

Methods: A descriptive process analysis of identified obstacles and solutions in all phases of the evaluation. Work notes, minutes from the steering group and the evaluating group meetings where analyzed to recapture the evaluation process.

Result: PT was used to get an understanding of the components of the policy, the projects and their interrelations. Three separate PT where developed, one for the CC policy and one for the project in each municipality. To get a general idea of the projects and to organise the vast amount of documentation a form was developed for the project managers to fill in. To identify stakeholders and actors, organisational charts (OC) were developed for the project’s organisations including CC representatives. The evaluation’s data collection was based on principles for triangulation (documents, survey and interviews). The PT and OC where used in the purposeful sample of respondents. The PT and OC also worked as a component when reporting the results.

Conclusion: PT is a useful tool to clarify the intentions and relations between levels of implementation when evaluating complex, multilevel programs. Using multiple means for data collection is a helpful strategy to generate both general and in depth understanding of a policy’s implementation. PT and OC are useful tools to make sure everyone has the same understanding of the policy’s components and organisation when communicating with stakeholders and respondents in all phases of the evaluation process.