In the face of multiple global crises such as climate change, a transformation towards sustainable development is more urgent than ever. Digitalization, as a fundamental change in society and the economy, offers great opportunities for sustainable development, but also poses its own threats, as evident in the immense resource consumption and growing surveillance tendencies. To leverage digitalization for sustainability transformation without compromising it, software engineering requires a significant shift in practices and structures. However, research in this area is still immature, lacking a deeper understanding of sustainability, its application in practice and solid engineering approaches. To bridge these gaps, this thesis aims to operationalize sustainability by proposing sustainability goals for software engineering, followed by the development of novel assessment methods and appropriate tool support.