Ultrasound imaging, which uses sound waves to create images of tissues and measure blood flow, is a widely accepted noninvasive diagnostic tool in both human and veterinary medicine. Advances in technology have expanded its use to smaller animals, such as rats and mice, allowing for detailed imaging of organs like hearts and kidneys and the evaluation of tumors. Ultrasound biomicroscopy offers even higher resolution, useful for studying mouse embryos. Other techniques, such as contrast-enhanced imaging and intravascular ultrasound, further enhance its capabilities. This paper highlights ultrasound’s basic principles, equipment, and applications, noting its significant impact on refining and advancing research methods involving small animals.