The ultrasound transducer (probe) is the primary interface between the imaging system and the patient. It contains piezoelectric crystals that convert electrical energy into high-frequency sound waves and convert returning echoes back into electrical signals. Transducers come in many configurations — linear, curvilinear, phased array, endocavitary, and others — each optimized for specific anatomical regions and clinical applications. Transducer frequency, footprint, and focal zone are key selection factors.