Biodiversity is an umbrella term to describe collectively the variety and variability of nature. It encompasses three basic levels of organisation in living systems: the genetic, species, and ecosystem levels. Plant and animal species are the most commonly recognized units of biological diversity, thus public concern has been mainly devoted to conserving species diversity. (Source: WRES/GILP96)

Biodiversity includes all living organisms found in the atmosphere, on land, in the soil and in water, their genes,their communities and the habitats and ecosystems of which they are part. All species have a role and provide the fabric of life on which humanity depends: from the smallest bacteria in the soil to the largest mammal in the ocean. The dynamics of species and habitats are interrelated with the water cycle,
the mineral cycle and the energy flow. These processes together determine the state of ecosystems that people manage and on which they depend. (Source: EEA, SOER 2010, Biodiversity Thematic Assessment, http://www.eea.europa.eu/soer/europe/biodiversity )