A transition toward sustainable lifestyles and changing individual behaviour plays a crucial role in tackling global challenges such as climate change. Spillover effects describe when one environmentally sustainable behaviour (ESB) leads to another, often initiated by a behaviour change intervention. Thus, studying spillover effects is a promising approach to better understand the holistic relationship between ESBs within and between different contexts (e.g. work, home). Based on identified literature gaps, this thesis addressed the following research questions: (1) “How does a behaviour change intervention in the workplace affect environmentally sustainable behaviours at home?” (2) “What role does identity play in the emergence of positive and negative contextual spillover effects (or a lack thereof)?”. Building on Identity Process Theory, a theoretical framework was proposed that explains positive, negative, and a lack of spillover.

A mixed-methods approach was used to assess spillover from work to home by evaluating the effects of a meat reduction intervention in a workplace on employees’ ESBs at home with an intervention-control group design. In a private sector company, 82 employees were surveyed and 26 semi-structured interviews were conducted. A multinomial regression was used to analyse the quantitative and template analysis to analyse the qualitative data.

The findings provide evidence for both positive and a lack of spillover effects. The quantitative results showed no change in red meat consumption at home nor in other, related ESBs at home. The qualitative data analysis, on the other hand found positive contextual spillover effects (e.g. increase in local food consumption). Furthermore, identity was found to play an important role for positive spillover effects, which was found both in the quantitative and qualitative data.

Theoretical and practical implications are discussed, including future research. This study provides insights into contextual spillover effects from a behaviour change intervention at work to ESBs at home.