This chapter presents a review of studies on the establishment of artificial associations with isolated protoplasts as well as with cultures of higher plant cells and tissues. The studies on producing artificial associations with cyanobacteria were carried out in parallel with similar investigations using other microorganisms. The establishment of associations based on isolated protoplasts or cultured cells of higher plants, on the one hand, and microorganisms, on the other, is regarded at present as one of the new methods of modifying plant cells or whole plants. Photosynthetic eukaryotes have evolved via the formation of associations between photosynthetic prokaryotes and heterotrophic microorganisms. The use of associations between the cultured cells of higher plants and nitrogen-fixing cyanobacteria would probably make it possible to understand the causes underlying the specificity of cyanobacteria in natural symbioses. Plant cells in culture retain their ability for the biosynthesis of secondary products characteristic of the whole plant.