Fiber Bragg gratings have found widespread application in sensor systems, e. g. for temperature, strain or refractive index measurements. The concept of fiber Bragg gratings allows also in a simple way the realisation of arrays of such sensors. The development of such optical fiber sensor systems often requires special fibers and grating structures which may go beyond more conventional Bragg grating structures in typical communication fibers. Concerning fibers there is, for example., a need of achieving fiber gratings in small diameter fibers and fiber tapers as well as in microstructured fibers. Special fiber grating structures are of interest e.g. in the visible wavelength range, which requires smaller spatial structures compared to more conventional gratings in the near infrared wavelength region. Examples for such modern developments in fiber Bragg grating technology for sensor applications will be presented and discussed.