One of the commonest bluets in Denmark and Europe, together with Common Bluet.

Imagos perhaps flying a bit later than also common species Variable Bluet which it looks a lot like.

Azure has short black lines on the side of the thorax and the shape of the black marking on S2 is resembling a horseshoe, hence the Danish name. Also it generally does not have a pale bar between the eye-spots, but this feature is variable. The S2 marking is too, but probably to a lesser degree and therefore more reliable for identification purposes. The shoulder (antehumeral) stripe is rather broad but narrows toward the rear end while staying intact, whereas on Variable it often breaks; and looks like an exclamation mark.

The pronotum of the bluets is a diagnostic feature which among females often is the best way to separate them: Azure has a gently sloping curve with a wide central lobe.