This chapter focuses on the diseases associated with fatty infiltration of the liver: diffuse fatty liver and focal fatty infiltration and sparing of the liver. We detail the pathological features, imaging manifestations, diagnostic points, and differential diagnosis and focus on the use of imaging methods including ultrasound, CT, MRI, and PET/CT in the diagnosis of fatty infiltration of the liver. Ultrasound is the most commonly used diagnostic method at present to look at the morphology and echo features of the liver. CT diagnoses the presence of fatty liver through the density of liver parenchyma and CT values. MRI can directly quantify the fat content in hepatocytes, and chemical shift imaging can be used to show fat infiltration. PET/CT can assess glucose uptake and metabolism in the liver. These methods can complement each other to improve the diagnostic accuracy of fatty liver. In addition, this chapter describes emerging imaging techniques such as ultrasonic elastography, MRI-PDFF, and IDEAL IQ technology that could more accurately assess the extent and composition of fatty infiltration.