In recent years increasing environmental awareness has resulted in a sudden increase in interest in the environmental sustainability of software systems.The creation of the Green Software Foundation in 2021 helped to accelerate this interest by providing a focus and community for those interested in sustainable software development. However, we are still in the early stages of industry-wide adoption, with relatively few development teams actively prioritising environmental sustainability in their work. In this talk we will briefly review the history of sustainable software development in academia and industry, review the current state of the art in measuring the environmental impact of a software system. With the use of case studies, we will illustrate the significant effect that architectural decisions can have, positively or negatively, on a system's environmental sustainability, and explore some of the architectural techniques, tactics, and patterns that we can use to estimate and reduce the environmental impact of our software systems.