Recent results on optomechanical and optoacoustic nonlinearities in optical fibres are reported. In a new type of a microstructured silica fibre, comprising two ultra-thin closely spaced glass waveguides, an extremely high and optically broadband optomechanical nonlinearity is shown to occur. This nonlinearity originates from the optical gradient forces between coupled waveguides, can exceed the Kerr effect by many orders of magnitude and allows the formation of stable self-trapped optical modes that represent a novel kind of optical soliton. Furthermore, optoacoustic interaction via electrostriction in the micron-sized core of a photonic crystal fibre is studied. It is demonstrated, that coherent optically-driven acoustic waves, tightly guided in the core, can facilitate in-fibre dynamic optical isolation and all-optical switching.