In this work, we introduce the concept and delineate the fundamental principles of photoacoustic interferometry (PAInt), aiming at the development of a novel methodology for the precise assessment of the speed of sound in liquid media. The PAInt apparatus integrates an intensity-modulated continuous wave laser beam at 20 MHz for the efficient generation of monochromatic photoacoustic wavefronts which interfere across the surface of a vertically displaced spherically focused piezoelectric element. In this context, the resulting interference pattern can reveal the acoustic wavelength in the liquid medium with remarkable accuracy, providing thus reliable estimations of the speed of sound in reference liquids (error ∼0.1%) such as distilled and sea water, acetonitrile, and ethanol.