The complexity of the sustainability challenge calls for participatory processes to support the large-scale collaboration across sectors and disciplines that is needed. Besides tools and methodologies to design these processes, the inner world of sustainability practitioners facilitating them is a key element for their success. This thesis focuses on the role of self- awareness for sustainability practitioners based on their stories of having to adapt their process design, their personal practices and advice they give. Using semi-structured interviews with facilitators who use Theory U and/or Art of Hosting methodologies to facilitate participatory processes for sustainable development, we found that self-awareness supports sustainability practitioners in practical terms on the spot, in their leadership development and in the effectiveness of their work. Moreover, through self-awareness, they recognize the importance of diversity and trust, essential elements for the adaptive capacity of the group. This recognition could contribute to more successful processes and outcomes, making practitioners' work and contribution to addressing the sustainability challenge more effective. The potential analogy between inner worlds and healthy social systems poses an interesting angle for further research. Is there such a thing as an inner dimension of sustainability? How does self-awareness relate to that?