Environmental certification of buildings plays an important role in reducing the impact of our buildings on the environment. When certification systems have been created, it has been done with the aim of creating and developing properties that will reduce their environmental impact and be climate-friendly. Environmental certification schemes largely assess the performance of the building, rather than the well-being and health of those who use it. The International WELLBuilding Institute realized that a separate system focusing on people was needed and in 2014created the WELL Building Standard health certification system. WELL is a certification system for buildings with the aim of putting people and the environment as its focus. This thesis work has been carried out in collaboration with Sweco and the aim of the report is to investigate how to go about certifying an existing building with the WELL Building Standard, and whether and how WELL differs from the other Swedish certification systems. The methodology of the study is interviews with representatives from the industry and a direct observation. A literature review has been conducted on WELL and other Swedish certification- and regulatory systems. Using this, a result has been produced that can help companies and building owners understand what WELL means and how it can be applied to existing buildings. Out of the total 11 indicators in WELL, five indicators are assumed to be easier to achieve and two are assumed to be more difficult to achieve. In the remaining four, there are both easy and difficult indicators to score in. The conclusion of this study is that the most important thing is to check the performance of the building, to know how to proceed with the challenging indicators. Handling time is the main difference in management between WELL and other certification schemes, which is due to two factors: annual monitoring and lack of knowledge. The conclusion that can be drawn is that it is mainly due to the 24 mandatory requirements of WELL, where several must be accounted for and reported every year. The study also shows that a Swedish version of WELL will not be constructed in the closest future