There are currently 36 recognized biodiversity hotspots. These are Earth’s most biologically rich—yet threatened—terrestrial regions.

To qualify as a biodiversity hotspot, an area must meet two strict criteria:

• Contain at least 1,500 species of vascular plants found nowhere else on Earth (known as "endemic" species).
• Have lost at least 70 percent of its primary native vegetation.

Many of the biodiversity hotspots exceed the two criteria. For example, both the Sundaland Hotspot in Southeast Asia and the Tropical Andes Hotspot in South America have about 15,000 endemic plant species. The loss of vegetation in some hotspots has reached a startling 95 percent.

 First defined in 1988 by scientist Norman Myers, biodiversity hotspots are areas characterized by high levels of endemic plants coupled with significant habitat loss. Specifically, a region must meet the following criteria to achieve Conservation International’s hotspot classification:At least 1,500 species of vascular plants (0.5% of the world’s total) are endemicAt least 70% of the original natural vegetation has been lostWhen Myers first defined the term, he identified 10 tropical forest hotspots. The need to pinpoint priority conservation regions led Conservation International (CI) to adopt the term and reassess the hotspot concept. In this process, CI introduced quantitative thresholds (see above) and added additional regions. At that time, there were 25 hotspots. Because of the constant change in environmental threats and the improved understanding of biodiversity, CI has since revisited the hotspots to refine boundaries, update information, and add new regions. This process produced an additional 10 hotspots, bringing the total to 35.