Abstract: An acoustic wave device includes: a substrate; a first electrode on the substrate; a piezoelectric layer on the first electrode; and a second electrode on the piezoelectric layer. A bonding interface is located between the substrate and the first electrode. The full width at half maximum (FWHM) in the X-ray diffraction pattern of the crystal plane <002> of the piezoelectric layer is between 10 arc-sec and 3600 arc-sec.