The acousto-optic effect has been successfully used since the early 80's in the design and construction of a variety of conventional optical fiber devices such as frequency shifters, couplers, filters and modulators. Acoustic waves can be employed to modulate the spectrum and switch the wavelength of conventional fiber Bragg gratings as well as for controlling the Q-switching in distributed fiber lasers. Tunable devices induced by acoustic waves have also been demonstrated in photonic crystal fibers (PCF), whereas a resonance dip corresponding to an excited cladding mode can be tuned over the wavelength. In a similar work, but inducing an acoustic excitation over the longitudinal axis, long period gratings can be created in the transmission band of a solid core PCF. Recently, the availability of Bragg gratings in photonic crystal fibers enables several applications, particularly if their properties can be controlled in order to produce modulation or allow tunability. A way of achieving these effects is through the excitation of acoustic waves in the fibre, which allows a rapid method for shifting or modulating tie Bragg wavelength. In this work the application of acoustic-waves to microstructured fibers is reviewed and recent results on the modulation of fiber Bragg gratings in photonic crystal fibers are presented.