Algae are genetically and physiologically heterogenous group with different nutritional strategies. Historical division on autotrophic and heterotrophic organisms can not be applied to a huge number of species, while the contribution of mixotrophy often went unrecognised. Mixotrophy entails the ability to conduct both autotrophic (mostly photosynthetic) and heterotrophic lifestyle. A wide nutritional spectrum exists considering the accumulation of carbon, but also of other important minerals such as nitrogen, phosphorus, iron and vitamins. Specifically, organisms can be divided into: 1) primary phototrophs with additional heterotrophic ability, 2) primary phagotrophs. and 3) obligate mixotrophs demanding both light and prey, with many other cases in-between the three aforementioned. Mixotrophy exists among numerous species of cyanobacteria, Chrysophyta, Haptophyta, Dinophyta and Chlorophyta. Some of these species are important because of their role in forming toxic algal blooms, while others have a significant contribution in the global cycling of carbon and other elements. This review presents various groups of algae with different levels of mixotrophy, as well as methods used for studying this phenomenon.