Phycosynthesis or algae mediated iron nanoparticle synthesis presents a sustainable, eco-friendly and non-toxic approach to keep up with its expanding applications. Cyanobacteria and algae -the photosynthetic cryptogams with high growth rate, wide range of cell types and simple harvesting procedure, serve as favoured organisms for nano biosynthesis. Generally zerovalent iron nanoparticles along with different oxides with varied morphology like -rod, spherical, spindle and cubes are produced by these bioreagents. Chemically iron oxides like Fe2O3, Fe3O4 and hydroxide FeOOH are produced in nano forms by cyanobacteria, microalgae and seaweeds in an eco-friendly environment. Upon exposure to a precursor solution, the biomolecules present in these organisms act as reducing and capping agents, resulting in nanoiron production. For microscopic unicellular algae, live cell suspension-mediated intracellular synthesis is frequently favoured, and macro algae like seaweeds are used as cell free extract to stimulate extracellular production. More than ten phaeophycean species have been discovered to produce iron nanoparticles in cell free extract conditions. Different genera from different phyla of algae are capable of producing nano iron particles as reported so far. The exposure time and other reaction parameters like pH, temperature, etc. define the physicochemical characteristics of nanoparticles which determine their unique application. Some applications include biomedical technologies, removal of heavy metal contamination, solving agricultural issues catering to the food and energy demand and iron shortage in the human population. This study summarises the results of the last fifteen years of investigation on the phycosynthesis of nanoiron-which expanded significantly over the past five years. All rights reserved, Elsevier.