Tamil Nadu is India's fifth largest producer of rice, next to West Bengal, Andhra Pradesh, Punjab and Uttar Pradesh. The Cauvery delta region of the composite Thanjavur district in the state is known as the Rice Bowl of South India. Rice is grown in 2.1 million hectares accounting for about one-third of the gross cropped area under diverse environments in the state, like; rain-fed tank, tank, tank cum well, canal (river) and canal (reservoir) irrigation systems. The rice productivity growth had been declining at the rate of -0.40 per cent (during period 1990-91 to 1999-00) as the yields of existing varieties had already been plateauing. Recent breakthroughs in the development of tropical hybrid rice technology had how ever provided an alternative option for raising yield levels for sustained production growth in rice especially in favourable irrigated eco-systems. A nation-wide network on Development and Use of Hybrid Rice Technology - initiated by the ICAR with support from the UNDP,FAO and IRRI. Under this network,TNAU has released four rice hybrids so far, namely; CORH 1, CORH 2 ADTRH 1 and ADTRH 2.Hence, it was decided to take-up this hybrid technology impact study.