Consumers have an impact on the sustainability status of our world in many different ways. In this project the focus lies on food consumption. Dietary changes are considered a great opportunity for fighting climate change, especially through the reduction of meat consumption (Poore & Nemecek, 2018). This graduation project is performed for Goodcase. The startup aims to accelerate the shift towards a sustainable diet by offering sustainable foods directly to the customer. The goal of this project is to empower food box customers to switch their diet to a more sustainable one by offering a support system that promotes long-term behaviour change. Literature research indicated that selfefficacy and social norms play the main role when it comes to changing to more eco-friendly diets (Eker et al., 2019). Lead users reported that they had initially increased their self-efficacy to switch to a new diet by challenging themselves to perform the new behaviour for a certain time. Therefore, the design solution focused on self-experimentation through self-challenging, paired with the facilitation of social interaction with other users online. This combination is also applied in other behaviour change services, e.g. the Weight Watchers programme which helps consumers to eat healthier. Based on these key insights, the design brief defined the following design goal: To increase the self-efficacy of consumers trying to change to a more environmentally sustainable diet by facilitating self-experimentation with a food box. Following this brief, a productservice system was designed which consisted of a food box with products facilitating vegetarian cooking, a physical guide that challenged users to reduce meat consumption, and an online group for users to motivate each other. In a subsequent user test, qualitative research with eight consumers suggested that the food products triggered experimentation with vegetarian food which helped consumers to increase their selfefficacy to eat less meat. Vegetarian eating might have been positively influenced by the meat reduction challenge. However, many users found it too inconvenient to monitor themselves daily with the guidebook. Finally, a second iteration of the design concept is proposed that incorporates the key learnings from the user test. The concept, called EcoEat, combines a food box with a supportive app which allows users to monitor and improve their behaviour over the long term and in a more convenient way. This design proposal could be tested in the future. The main conclusion from this project is that providing real experiences with unfamiliar, eco-friendly food products can positively influence the consumer’s attitude towards sustainable diets. It can open them up towards trying out more food of this kind and thereby helps them to switch to a more sustainable diet. More of these opportunities for trial should be provided to consumers. Food boxes are a good medium to provide these experiences regularly. With a complementary behaviour change service the experimentation with a sustainable diet can be upheld if the users are guided in a way that is convenient for them.