It is 62 mm long. Both sexes have azure blue spots on each abdominal segment and the thorax also has azure markings. The markings on the male are brighter and more conspicuous than in the female. The female also has a brown colour form. This species flies in sunshine, and will also bask on stones or tree trunks. It shelters in heather or similar low vegetation in dull weather. The flight period is from late May to August. 

The Azure Hawker is a relatively small aeshnid, similar in size to the Blue-Eyed and Migrant Hawkers (Aeshna affinis and A. mixta). Its thorax is essentially brown, with short and weakly-developed antehumeral stripes, while the spots on its abdomen are a bright blue in the male and usually yellow in the female. Aeshna caerulea occurs at high latitudes (in Scandinavia and Northern Scotland) or, in Central Europe, at high altitudes (in the Alps and Dolomites). To survive in such cold conditions it has the typical habit of basking on bright and flat surfaces, by pressing its body against e.g. the bark of a birch tree. Failing that, e.g. above the tree line in the Alps, its preferred perch is a sun-exposed rock. The species also has the capacity - maybe more than any other European dragonfly species - of regulating its body heat by changing the colour of its abdominal spots. When it's warm and sunny, those spots are typically light blue in the male; when it's cloudy and cold, the spots are a much darker, duller, chocolate brown colour. Dark colours absorb more light than light colours, and light-absorption helps to generate body heat. 

This species can be found in alpine and arctic moors, heaths and tundra. It breeds in bog pools and sedge swamps, and is seldom found below 1,000 m in the Alps. 
There are a number of conservation measures already implemented for Aeshna caerulea, including monitoring its population trends and range. However restoration and conservation of its habitat are required as it is declining in some areas of its range, particularly in central Europe. 

IUCN Red List access as Least Concern. The species is widespread in the Eurasian polar region. Though locally scarce and declining, particularly in central Europe, as a post-glacial relict and thus listed in threat categories of regional red lists.