This dissertation investigates the psychological and behavioral strategies that influence pro-environmental decision-making, combining insights from controlled experiments and a longitudinal field study. The research explores how decision support, framing effects, and defaults can promote sustainable behaviors, providing a comprehensive understanding of the factors that drive environmentally friendly choices. The first study uses a controlled online experiment to demonstrate how a transparent decision support environment, featuring real-time colored feedback, enhances pro-environmental behavior. Participants in the decision support condition were more inclined to prioritize environmental outcomes over financial gains in the Carbon Emission Task, underscoring the effectiveness of decision aids in promoting sustainable choices. The second study delves into the concept of ”coherently arbitrary” pro-environmental behavior, revealing that environmental decisions are often influenced by arbitrary contextual factors rather than consistent preferences. This study extends behavioral economic findings to environmental psychology, highlighting a motivation-impact gap where environmental intentions do not always result in corresponding actions. The third study examines the role of gain-loss framing in voluntary pro-environmental behavior through an online experiment. Findings indicate that loss framing can slightly increase pro-environmental efforts, suggesting the potential of tailored communication strategies to enhance environmental engagement. The final study presents a longitudinal field investigation of green energy defaults in a significant moment of change. Analyzing data from 143,313 meters over multiple years, this study reveals that green energy defaults maintain high adherence rates, even amid a merger and moderate price changes. The results underscore the stability and effectiveness of default settings as a policy tool to encourage sustainable energy consumption. Together, these studies contribute to a better understanding of the psychological factors that influence pro-environmental behavior and suggest possible approaches for encouraging sustainable practices.