The propagation properties of microstructured optical fibers useful for sensing applications are reviewed. The interaction between light and sample can reach 95 % in singlemode hollow core fibers and examples of structures exhibiting such large overlap ratios are described. The generation of 300 nm and 700 nm flat continua of visible and IR light in a single highly nonlinear holey fiber, well suited for the detection of biological species by spectroscopy, is reported. The low temperature sensitivity of long period gratings and of the birefringence in holey fibers is attractive for sensors operating in varying environmental conditions.