Predominant sustainability pedagogy and science largely focus on fixing existing problems via solutions external to humans (e.g. carbon sequestration, renewable energy). While external or outer interventions can support a transition to a sustainable future, internal or inner developments should also be highly valued. For this dissertation, I define sustainability as the ability of any individual, community or country to meet their needs and live happily without compromising the ability of other individuals, communities, countries and future generations to meet their needs and live happily. Framed this way, a sustainable and happy life should focus on both outer and inner development, the latter largely unconsidered in sustainability science and scholarship. I propose that emphasizing spiritual wellbeing and spiritual practices can support individuals and communities to act with mindfulness, awareness, compassion, connection, and love, transitioning to a more sustainable existence. This dissertation consists of three studies: (1) the development of a theoretical framework identifying spirituality as the missing link between sustainability and happiness, (2) an empirical pilot study testing the theoretical framework via contemplative practices in a sustainability classroom, and (3) an autoethnography exploring my inner development and transformation as a sustainability and spirituality researcher over the past four years. The theoretical framework found and posits, based on existing literature, that spirituality indeed may be the missing link between an unsustainable existence and a sustainably and happy future. Results from the empirical study suggest that a focus on spirituality leads students to develop inner traits necessary for sustainable behavior and a deeper understanding of sustainability. My autoethnography demonstrates the spiritual transformation possible from integrating spiritual well-being and intellect, while striving to embody sustainability as a spiritual journey. My research supports further studies and a greater understanding of the importance of spiritual well-being to sustainability and the incorporation of contemplative practices in sustainability classrooms. Finally, I hope this dissertation will (1) inspire sustainability scientists, researchers, and students to integrate spiritual well-being as an important part of their lives and work, and (2) encourage deeper conversations about the radical inner shift we need to achieve lasting sustainability for all beings. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]