Ascidians with rapid growth rate and sexual maturation are important benthic organisms in marine ecosystems and are also one of the major fouling groups. Following colonization on aquaculture facilities, ascidians cause a series of problems such as competing food and settlement substrata with the cultivated species, blocking netting holes, increasing the weight of cages and retarding water flow, leading to the deterioration of the aquaculture environment. Growth and quality of those cultivated species will therefore be negatively affected. To date, a total of 103 ascidian species within 29 genera and 9 families (Ascidiidae, Cionidae, Clavelinidae, Didemnidae, Molgulidae, Perophoridae, Polyclinidae, Pyuridae and Styelidae) are identified from fouling communities worldwide. Of them, the dominant species are the solitary ascidians Ascidia sydneiensis, Phallusia nigra, Botryllus schlosseri, Diplosoma listerianum, Styela clava, Symplegma brakenhielmi, Herdmania momus, Microcosmus exasperates, Molgula manhattensis, as well as the compound species Ciona intestinalis. The distribution of fouling ascidians is highly relevant to geographic locations. Of them, 64 species were found in the Pacific Ocean, 23 in the Indian Ocean, 44 in the Atlantic Ocean and 3 in the Arctic Ocean. In the Pacific Ocean, the most common species are Styela plicata, S. canopus, Ciona intestinalis, Microcosmus exasperatus, Diplosoma listerianum, Molgula manhattensis and Ascidia longistriara. Moreover, the species A. sydneiensis, Phallusia nigra, Botryllus schlosseri, Diplosoma listerianum and Symplegma brakenhielmi are found in the Indian and Atlantic Oceans, whereas, Styela rustica is the dominant fouling species in the Arctic Ocean. Season is a major factor affecting ascidian fouling. Summer is the settlement peak in the Pacific Ocean, however, in the Indian Ocean the highest ascidian fouling biomass occurs in spring and autumn. In addition, larval settlement of different ascidians presents distinct preferences for substrata. On floating units, Phallusia nigra and Ascidia cannelata were generally abundant, whereas Herdmania momus preferred to settle on horizontal surfaces of submerged objects. Current methods for fouling control more or less have some limitations in practical applications. Understanding gene regulation on the ascidian larval metamorphosis process may provide an effective way to develop novel antifouling technology. Moreover, by studying fouling communities colonizing various artificial facilities, the influences of alien ascidians on local biodiversity can also be elucidated. Compared with traditional morphological identification, DNA-based methodology might solve the problems on taxonomy of related ascidians. Biofouling can alter the substratum surface microenvironment and affect the corrosion processes of materials. Thus, the effects of fouling ascidians, particularly compound species, on material corrosion deserve further study. At present, most work on fouling ascidian investigations is limited to tropical and temperate zones, particularly in shallow waters. To thoroughly elucidate species compositions, biodiversity, distribution, population dynamics and role of ascidians in fouling communities, further studies should be extended to the polar regions and even deep water.