Any fertilizers involving living organisms, or the products obtained from living organismscan be REFERRED to as biofertilizer, although nowadays, the term isgenerally used for living organisms usedfor fertilizer purpose.Various micro-organisms are present in soil and they play an important role in helping plants to grow.A handful of soil has several milions of bacteria - mostly saprophytic - converting organic wastes in soil into soluble sources of nutrients for plants. Their activity also makes nutrients in soil available - solubilization of phosphates for example. Enzymes released by fungi such as MYCORRHIZAE can convert rock phosphates into soluble phosphates. Some microbes makeit DIFFICULT for pathogenic micro-organisms to affect plants.The most important nutrient for plants - Nitrogen - is “fixed” ie,converted from gaseous form to soluble form such as ammoniacal radical by various “nitrogen-fixing” bacteria. Someof these are independent. others are symbionts. If the population of such microbes in soil is high, the nitrogen requirement of a plant crop can be signiifcantly met by their activity.Scientists have identified a variety of such micro-organsims that provide some important input to plants.Use of biofertilizers isbenefical for a varietyof reaosns - they are ECONOMICAL, and also ecologically sustainable.Hence steps to promote their use in agriculture are indeedimportant.Only as a sample - certainly not an exhaustive list - here are a few mico-organisms that can be called biofertilizers.Various cyanobacteria -Nostoc, Anabaena.- some are free-living, others are symbionts.Rhizobiumspp - can live freely, but can do significant quantities of N-fixation when they form root knot nodules with their specific host leguminous plants.Mycorrhizae -Glomusfasciculatus.Azotobacter- free livingN-fixation.