Irrigated agriculture constitutes about 20% of the total cultivated land in the world, has much higher crop productivity compared to rainfed agriculture and contributes significantly to meeting the challenge of feeding the world. However, water resources are very limited, especially in the arid and semi-arid regions where irrigated agriculture is most practised. This chapter describes how fertigation (application of nutrients through irrigation water) acts as a powerful and efficient tool to optimize the efficient use of both water and nutrients. The chapter examines the advantages and limitations of fertigation, the prerequisites for successful and efficient fertigation, and the equipment available for fertilizer injection. The chapter also covers fertigation under greenhouse conditions and how the principles of the ‘4 rights’ (4R) can be applied to nutrient stewardship. Finally, the chapter addresses monitoring of soil, plant and water under fertigation, and looks ahead to future research in this area as well as providing guidance on further reading.