On 14 February, the UK government is hosting an international conference on the illegal trade in wildlife, at which it hopes to obtain high-level political commitment from governments around the world to fight the issue.
According to the government, the illegal wildlife industry is worth more than £6bn each year, and it is growing. Rhino horns can sell for up to £40,000 ($65,000) per kg, making it more expensive than gold. According to Cites - the Convention on the International Trade in Endangered Species - more than 22,000 elephants were slaughtered for their tusks in 2012.
Of course, the issue is not just confined to ivory; many other endangered animals are in demand, either for their perceived medicinal properties or as a status symbol.
Photographer Patrick Brown spent 10 years documenting the illegal trade of endangered animals in Asia and, on the eve of the London conference, the work has been published by Dewi Lewis.
Brown's pictures explore the whole story, from the poachers and those trying to protect the animals, through to the dealers and buyers.