Behaviour Study of Tomato Lycopercicum esculuntum Mill. and Red Pepper Capsicum annuum L. Crops under Greenhouse Conditions Conducted in Single and Twinned Rows. Tomato (Lycopercicum esculuntum Mill.) and red pepper (Capsicum annuum L.) crops under greenhouse conditions and drip irrigation are widely developed in Tunisia. Although, it is known that drip irrigation permitted some water savings. Other cultural techniques such as single or twinned planting rows combined with drip irrigation system could improve the water management. In this aim we have conducted an experimental trial under greenhouse adopting drip irrigation with simple and double amounts of water and single and twinned planting rows. Some agronomic traits in the occurrence the height of plants, the fruit number and yield per plant, the precocity and the water efficiency were studied. The red pepper culture with a spacing of 80 cm between lines, gave the best results in the simple row and simple amount of irrigation treatment. On the other hand, tomato, in twinned rows (90 cm among rows) with double amount of water gave the best reaps in yield and more precocious. Whereas the higher water irrigation efficiency was obtained for the treatment combining the twinned planting rows and simple amount of water.