The use of less invasive technologies to determine the body composition of pigs during growth is important for nutritional, breeding and management purposes. Nowadays, technologies based on ultrasound, X-rays and nuclear magnetic resonance are available and can be used either directly on the farm for selection or strategy decisions, or in a laboratory for research purposes. This chapter describes the most common non-invasive technologies used to characterise body composition, addressing the aspects to consider for both the preparation of the animals and the acquisition and analysis of measurements. It also considers the differences between techniques and the information that can be obtained from each technique.