All microbes are not pathogenic, many of them are beneficial to human beings. We use microbes and their derived products almost every day. Lactic acid bacteria convert milk into curd. Saccharomyces cerevisiae (yeast) is used in bread making. Idly and dosa are made from dough fermented by microbes. Bacteria and fungi are used in cheese making. Industrial products like lactic acid, acetic acid and alcohol are produced by microbes. Antibiotics are produced from useful microbes to kill the disease causing harmful microbes. For more than a hundred years, microbes are being used to treat sewage by the process of activated sludge formation. Bio-gas produced by microbes is used as a source of energy in rural areas. Microbes are also used as bio-control agents to avoid the use of toxic pesticides. Now a days chemical fertilisers are gradually replaced by bio-fertilisers. In bio-remediation naturally occurring or genetically engineered microorganisms are used to reduce or degrade pollutants.