In 2002, 188 countries signed the Convention on Biological Diversity - thus committing themselves to slowing the loss of biodiversity by 2010.
But with just a few years to go, there's no agreed way of measuring progress towards that goal.
How can we find out if all our efforts to save species and environments are making any difference?
And what do we mean by biodiversity? Biologists say it's much more than just the numbers of plants and animals that fill our world and make it unique.
It's also the range of genes, habitats and their multiple interactions.
Sue Broom attempts to untangle the term, and discovers why biodiversity is so important and why it must be maintained.