The internal quality of agricultural products is an important attribute that is considered by consumers when buying them. Grading agricultural products according to their internal quality, is an effective way to make the best use of the products, and thus improve the overall value. In recent years, several nondestructive, intelligent sensing techniques have been studied extensively for detecting the internal quality of agricultural products, including Vis/NIR spectroscopy, multi-/hyper-spectral imaging, nuclear magnetic resonance and imaging, X-ray and computed tomography, electrical nose and acoustic technique. In this chapter, the working principle of each technique is provided, and corresponding applications in the agricultural domain are reviewed to provide overall understanding of these techniques. The challenges and perspectives of these techniques are also analyzed.