Carbon markets – both emission trading systems and baseline and credit systems – are an increasingly common policy instrument being introduced to address climate change mitigation. However, their design is crucial to ensure that they deliver cost-effective emission reductions while maintaining environmental integrity. This Element puts together a comprehensive, principle-based overview of the risks and abuses to environmental integrity and cost effectiveness that have emerged for carbon markets at all jurisdictional levels around the world, provides concrete examples, and offers effective policy and governance solutions to overcome such risks.