In The Netherlands there are two species of demoiselles, the Banded Demoiselle and the Beautiful Demoiselle. These dragonflies are seen along small rivers and streams, the male specimens clearly noticeable by their striking blue wings. The ecology of both species is described, bringing forward the importance of water quality of the streams, stream stucture and vegetation. Gaining and defending a territory along the water's edge is a necessity for the male demoiselles to reproduce. Courtship behaviour which follows is quite spectacular. The male flutters around the female, now and then dropping down into the water to flow along with the current. Numbers of Banded Demoiselles and Beautiful Demoiselles have decreased due to canalization and deteriorating water quality. Improved water quality has led to a recovery of the Banded Demoiselle, but not the Beautiful Demoiselle which has higher demands as to water quality and stream structure.