First successful classical biological control of a weed (prickly pear) was achieved unintentionally in India when cochineal insect, Dactylopius ceylonicus was mistakenly introduced from Brazil in place of D. cacti to produce dye from Opuntia vulgaris. This incident led to biological control of weeds. From 1863 to 1868, it was introduced to southern India, which was first successful intentional use of an insect to control a weed. In 1926, D. opuntiae, a North American species, was imported from Sri Lanka and its colonization resulted in spectacular suppression of Opuntia stricta and related O. elatior. So far in India, about 30 exotic biological control agents have been introduced against weeds, of which six could not be released in the field, 3 could not be recovered after release while 21 were recovered and established. From these established bioagents, 7 are providing excellent control, 4 substantial control and 9 partial control. Biological agents, mainly insects provided excellent biological control of prickly pear, Opuntia elatior and O. vulgaris by D. ceylonicus and  D. opuntiae; Salvinia molesta by weevil, Cyrtobagous salviniae; water hyacinth by weevils Neochetina bruchi and N. eichhorniae and galumnid mite Orthogalumna terebrantis; and Parthenium hysterophorus by chrysomelid beetle Zygogramma bicolorata. Some introduced bioagents did not prove success but providing partial control like of Lantana by agromyzid seedfly, Ophiomyia Lantanae, tingid lace bug, Teleonemia scrupulosa, Diastema tigris, Uroplata girardi, Octotoma scabripennis and Epinotia lantanae; Chromolaena odorata by Pareuchaetes pseudoinsulata; Ageratina adenophora by gallfly, Procecidochares utilis; submerged aquatic weeds such as Vallisneria spp. and Hydrilla verticillata in fish ponds by grass carp. There are many bioagents which have been introduced in other countries and have shown varying degree of success through combined effect. In Australia, 9 bioagents have been introduced against Parthenium alone. Such successful bioagents need to be introduced in India against some of the problematic weeds like Parthenium, water hyacinth, Pistia, alligator weed etc.