Fungi were considered terrestrial and oceans a “fungal desert”, however with considerable progress in marine fungal research made in the past two decades, fungi have surfaced as a ubiquitous component of the marine ecosystem. Particularly, planktonic fungi are now gaining recognition as an important component of coastal and pelagic realms of the ocean. Studies on fungal diversity, abundance and activity are providing insights into their role in marine ecosystem function. This presentation would focus on the abundance of planktonic fungi, methods to estimate abundance, the factors affecting their abundance based on the available literature on planktonic fungi from coastal and pelagic realms of marine ecosystem.