We live in a world in which chronic diseases are on the rise. Yet, improving personal health behaviours is a long-term goal, that is often undermined by alluring offers that provide instant gratification and other more pressing day-to-day matters. Often it is not the intention that is missing to change personal health behaviours, but there is much evidence that highlights a gap between what individuals intend to do vs. what they actually do (Sheeran, 2002). There are many existing behaviour change tools that provide the “solution” to a problem, yet no one solution will be effective for everyone (Hekler, Burleson, & Lee, 2013). Especially when considering health behaviours, that need to be sustained over time to have significant impact, it is prudent that interventions fit our goal, our ever changing lifestyle and are enjoyable (Phatak, 2019a). An alternative approach is to give individuals the tools to self-experiment with interventions, and through this, find interventions that work for them to establish a lasting effective behaviour change. This project explores self-experimentation (SE) as a method for helping individuals change their personal health behaviours. A research through design approach was used to answer the questions: (1) What is self-experimentation and why is it needed? (2) What does self-experimentation result in and how can it contribute to individuals achieving sustainable health behaviour change? And (3) how can design facilitate individuals to self-experiment? In alignment with these questions, this project yields three significant outcomes: First, a new take on self-experimentation was discovered; one that addresses the limitation of existing approaches and caters to the needs of people trying to change their health behaviours. User research into how people go about navigating their health behaviour, and the kind of evidence they need to make decisions revealed that: (1) People generally navigate their health behaviour through intuition. (2) People who practice self-experimentation, are not seeking to answer a hypothesis, but simply want to find an intervention that works for them, explore different options and learn about themselves in the process. (3) People can determine whether or not an intervention works for them simply by trying it out. This reveals if the intervention helps them achieve their goal (i.e. is effective), whether it fits into their lives and with their personality (compatibility) and whether they enjoy it. These insights created a premise for a new approach which was labelled “Explorative Self-experimentation”. It differs fundamentally from the existing “quantitative” method in that it omits the key ingredient of a data-driven scientifically rigorous objective evaluation of the effectiveness of interventions, and instead harnesses the intuitive evaluation formed by a user’s lived experience. By observing 14 participants undergo four weeks of self-experimentation, a set of 13 phenomena were uncovered that engaging with Explorative Self-experimentation results in. These can be summarised in five statements: Explorative Self-experimentation helps people (1) take incremental steps towards a long term goal, through (2) trial and error to success. It (3) leads people to get to the heart of the issue, (4) discover new perspectives and attitudes towards their own health behaviours and (5) find support along the way. These phenomena were linked to prominent behaviour change theories in the context of health in order to establish how explorative self-experimentation can contribute to individuals changing and maintaining their health behaviours. Finally, the research through design process involved creating three sets of prototypes that explore how to facilitate individuals to self-experiment with health interventions. The design process and the testing of these prototypes revealed three lenses from which to tackle facilitating self-experimentation: (1) designing for the process, (2) designing for different scenarios or stages of change and (3) designing for the underlying needs and values of people trying to change their health behaviours. As part of this third lens, I presented seven concrete starting points for designers to facilitate self-experimentation, linking the underlying values and needs to key ingredients design can provide. The compilation of these outcomes aspire to answer the research question of how design can facilitate SE: Designers can provide guidance through the process, designers can help initiate SE, help people maintain their efforts over time to find something that fits, or help turn fitting solutions into habits. Designers can cater to needs and values by providing guidance, incentives and inspiration over time, by making room for personal growth and flexibility, fostering personal attachment and by forming a resilient mindset. In conclusion, this thesis uncovers the potential of Explorative Self-experimentation and how to facilitate it. It presents a meta-strategy for helping individuals change and maintain personal health behaviours, and through this hopes to contribute to improving health both at an individual and societal level.