Many species of fungi including lichenized fungi (lichens) and algae have the ability to biosynthesize biologically active compounds. They produce, among others, polysaccharides with anticancer and immunostimulatory properties: (1) Background: This paper presents the characteristics of the most important bioactive compounds produced by fungi and algae; (2) Methods: Based on the example of the selected species of mushrooms, lichens and algae, the therapeutic properties of the secondary metabolites that they produce and the possibilities of their use are presented; (3) Results: The importance of fungi, especially large-fruited mushrooms, lichens and algae, in nature and human life is discussed, in particular, with regard to their use in the pharmaceutical industry and their nutritional value; (4) Conclusions: The natural organisms, such as fungi, lichenized fungi and algae, could be used as supplementary medicine, in the form of pharmaceutical preparations and food sources. Further advanced studies are required on the pharmacological properties and bioactive compounds of these organisms. Agaricales, Antioxidants/administration & dosage, Carotenoids/administration & dosage, *Chlorophyta, Diet/methods, Flavonoids/administration & dosage, *Fungi, Humans, Lichens, *Nutritive Value, Phytochemicals/*administration & dosage, Polyphenols/administration & dosage, Polysaccharides/administration & dosage, algae, biologically active compounds, functional food, fungi, mushrooms, pharmaceuticals sources