Abstract: A water pillow for coupling acoustic energy into tissue. The pillow is configured to conform to a transducer to facilitate coupling of ultrasound energy. The pillow includes a pouch that accommodates the transducer to enable a snug fit between the pillow and the transducer. The pillow includes a liquid inlet and outlet to facilitate liquid circulation for cooling, is biocompatible, has a low attenuation, is conformal to the shape of the transducer, facilitates use of an adjustable pressure to achieve various standoffs, includes an integral pouch to facilitate an interference fit to the transducer, facilitates water circulation for cooling, is sterilizable, and is disposable. Either the surface of the pillow adapted to conform to a tissue interface, or the surface of the pillow adapted to conform to the transducer, or both, can include pores configured to weep liquid to facilitate acoustic coupling of the pillow with the transducer and/or tissue.