Algae play an important role in soil life alongside bacteria and fungi. To deepen the understanding of soil-dwelling eukaryotic algae, a comprehensive identification guide that consolidates globally scattered data has been lacking. Over 1,000 species of algae have been described from soils, the air, and lichens, yet knowledge about their life processes, reproduction, development, etc., is still very incomplete. Additionally, many soil algae can only be captured through cultures. Therefore, this syllabus includes identification keys, descriptions of morphology and cytology with illustrations for 260 genera and more than 1,000 species of aero-terrestrial algae, along with supplementary information on occurrence, distribution, and existing cultures. A special chapter is dedicated to eukaryotic lichen algae. The systematic classification and arrangement provide a comprehensive resource.