This review provides a synthesis of the terrestrial symbiotic associations of soil algae, and the term cyanosymbiosis is coined as operational term for those in which cyanoprokaryotes (cyanobacteria) are involved. All types of associations (endo- and ectobiotic, intra- and extracellular, horizontally and vertically transmitted, bi- and tri-membered, including algae as mediators in complex guilds, natural and artificial, immobile and mobile) are presented with special attention to algal diversity and specificity of interactions with the host. Summary of peculiarities of symbioses of pro- and eukaryotic algae is provided before their more detailed description according to the hosts. The search for common features shows that the widespread presence among symbionts of resistant cell wall or protective mucilage sheaths around the cells and the ability to produce dormant cells (akinetes, aplanospores, and cysts) is a favorable feature for the vertical transfer of symbionts. The major difference between symbioses of pro- and eukaryotic algae, according to the available descriptions, is in their active or passive behavior: the active infection of host by the motile hormogonia of prokaryotic algae, which usually occurs in most of cases of endobiotic symbioses, contrasts with the “capture” by the host of eukaryotic algae, which remain “passive” during the infection or simply “land” on the surface of the host. Based on our expertise in algology and lichenology, we hypothesize that zoospores or planogametes of eukaryotic algae (commonly considered primordial features) may have played the role of active infectants in ancient times when symbioses emerged and propose to explore this topic more actively together with the possibilities for signal transmissions between the partners. Other specific traits of symbiotic algae along with some unresolved problems and perspectives for future research are also noted. Although it is a brief overview, this review mentions to novel methods and approaches in fundamental scientific research, but also those used for symbiosis formation with regard to the development of modern agriculture and biotechnology with the search for higher crops and specific natural products. When data allows, fossil symbioses are mentioned and attempt is made to outline the driving forces that have led to the establishment and maintenance of the special partnerships of algae with an extraordinary wide range of organisms, such as bacteria, other algae, fungi, land plants, and animals. In total, 89 algal genera from six phyla are discussed as real or potential participants of symbiotic interactions. This distribution of terrestrial symbionts reflects the general biodiversity of soil algae and their availability, which can be taken as other important “background” factors for establishment of symbioses. In this regard, absence of widespread streptophyte soil green algae from terrestrial symbioses allows to hypothesize also that evolutionary origin and age may be among the selectivity factors, assuming that ancient organisms had some very specific traits, which provided them with advantages to be chosen as partners during the establishment of the earliest symbioses.