What kind of software documentation a systems needs and how much documentation that is necessary are questions that has a lot of different answers depending on a number of variables. Traditional software development methodologies claims that software needs a lot of documentation and more agile approaches claims that it is better to write less documentation since most documentation is never used. According to studies a ratio of 11% of software projects costs are spent on documentation alone. The purpose of this study is to create a cost efficient software documentation strategy for an existing web system with a focus on deciding what information are relevant to document in order to keep a high ROI. This study was conducted as a single case study and made in collaboration with a company. The data collection was done by interviewing key people working in the system and doing participants observations. The result shows that information documented in a high level is what is most needed. Artifacts relevant to document are the source code, requirements of updates, functional tests, high-level architecture, reference manual and an end-user manual. The result also shows that new processes need to be implemented for the documentation strategy to be efficient. Recommendation for further research is to create a method of how to calculate the ROI for software documentation based on a number of organizational variables. / <p>Validerat; 20160615 (global_studentproject_submitter)</p>