This chapter focuses on the data needed for developing, testing, and applying crop and farm models. The chapter reviews the kinds of data available to crop and farm modellers. The chapter describes practices concerning storage, exchanging, and combining data from various sources, examining the socio-economic and ethical implications. The chapter looks at the role of companies in data flows and generating recommendations to farmers. The chapter presents examples of successful use of agricultural data, both for science and for agricultural practice. Finally, the chapter looks ahead to future research trends in this area.