ALARA (As Low As Reasonably Achievable) is the fundamental safety principle governing ultrasound practice. It directs sonographers and clinicians to use the lowest acoustic output (power) settings and the shortest exposure time necessary to obtain the required diagnostic information. ALARA is especially important in obstetric and pediatric imaging, during Doppler examinations over sensitive structures, and with any use of ultrasound contrast agents. Applying ALARA requires understanding which controls affect output — including output power, Doppler modes, and probe selection.