Geographically, Greece belongs to Southeastern Europe and to the Eastern Mediterranean region. It is the crossroad of three continents, namely, Europe, Asia, and Africa.

The geomorphology is diverse. Greece is primarily a mountainous country, with seventy per cent of its territory covered by mountains. It has a very long coastline, with a plethora of peninsulas and islands.

The climate is markedly influenced by the combination of geography and geomorphology. It is, broadly speaking, Mediterranean with rainy winters and dry summers. However, one encounters many specific climatic types ranging from the semi-arid and desert-like type of Southeastern Crete to the cold wet continental type of the Rodopi mountain range in the north, on the Greek-Bulgarian border.

The abiotic diversity, most notably the "mosaic" of micro-climatic types, is reflected in the presence of a highly diverse flora and fauna and a great variety of ecosystems.

The flora of Greece is composed of Mediterranean, Central European and Irano-caspian elements. Over 6,000 plant species have been recorded so far. There is a large number of endemic species relative to the size of Greece, due to the isolation of the numerous mountains and islands. In Europe, a higher number of species is found only in the Iberian Peninsula, where the flora also includes species of the Atlantic zone.

The fauna consists of a rich mixture of European, Asian and African species, including a considerable number which are endemic. The freshwater fish fauna is one of the richest in Europe: 107 species, of which 37 are endemic, in the standing and running water systems of the country. Moreover, 40 endemic subspecies have been recorded. The herpetofauna is also one of the richest in Europe, with at least 18 species of amphibians and 59 species of reptiles, approximately 60% of which inhabit the broader areas of the Greek wetlands. Greece is also important ornithologically. About 407 bird species have been recorded, of which 240 nest in Greece (59% of the total). Some species (e.g. Pelecanus crispus) nest only in Greece of all EU countries. The mammals of Greece include 116 species, of which 57 belong to IUCN endangered species categories. Finally, the number of invertebrate species has been estimated at 25,000, a very large number when compared to the country's small size.

The ecosystems range from the semi-desert like ones of Southeastern Crete to the cold climate mountain forests of birch, Scotch pine, and spruce. This variety often appears within small areas. For example, in a 150 km transect from the coasts of the North Aegean to the top of the Rodopi mountain one encounters ecosystems of Mediterranean, Central European and Scandinavian type.

A cardinal attribute of the terrestrial as well as the wetland-azonic ecosystems of Greece is that in spite of the often severe man-induced degradations, they maintain their pristine character to a considerable degree. Few countries of the European Union have such a high biotic diversity in a state so close to pristine conditions. Even the degraded forest and phryganic ecosystems keep, at least qualitatively, their natural structure.