Rare earth elements (REEs) have a crucial role in modern environmental and medical technologies, leading to a continuously growing demand for these elements. The relatively modest scale of the global REE mining sector means that the REE mineral deposit type knowledge base is small compared to more well-known styles of mineralisation. In this paper, we present a new classification scheme for differing REE mineral deposit types, outline the geological processes that cause REE enrichments, define characteristic grades and tonnages, and provide information on the environmental impact associated with REE mining, extraction and processing. Although current global REE supply is dominated by production from carbonatites, REEs are in fact found in a wide variety of deposits, including magmatic alkaline complex- and rhyolite-hosted REE mineralisation, REE-enriched iron oxide-copper-gold deposits, and REEs within heavy mineral sands, amongst others. Critically, REE mineralogy is linked to environmental risks during mining and refining, especially aspects such as radioactive U-Th, the use of harmful chemicals during processing and greenhouse gas emissions; future REE supply therefore needs to consider and address these environmental risks.