At last years EclipseCon Martin gave an introduction into the overall topic of sustainability in the context of software engineering. This talk dives deeper into one of the aspects: carbon offsetting. It is a widely used technique to deal with existing carbon emissions if they cannot be avoided upfront. And while this is generally seen as a good action towards making a positive impact to protect the climate, the devil is in the details. In this session, Martin will give an overview of carbon offsetting, explains briefly how that works, and talks about the details, including: different types of offsetting, how offsetting is being calculated, what that actually means, and why offsetting should only be a last resort.