This part provides an overview of existing empirical studies targeting sustainable software, with a focus on the design of the reported empirical studies, their key design decisions (together with a discussion of their benefits and drawbacks), and the various research methods and tools used in the literature. The learning objectives of this part include (but are not limited to): (i) to become familiar with the state-of-the-art, research results, trends, and challenges in the field of green and sustainable software and (ii) to critically reflect on existing research gaps and opportunities in the area.