In coastal waters the microalgae share the duty of primary production with the benthic algae, but due to their small size we need fine meshed nets to catch them. In the collecting glass the small algae will look like specks of dust, and we need a microscope to see them and identify the species. This present book is meant to be a short introduction to microalgal genera common in Norwegian waters, and illustrate what the species look like in the microscope. The book was originally published in September 2001, and the taxonomy of many species has changed. This edition, published in march 2019, is to some extent updated taxonomically, but also taking care of the relation to the «classical» algal literature.