The characterization of the fracture process zone inside a cracked concrete specimen is investigated through optical fiber technology. Fiber Bragg gratings are used to measure the strains in the close vicinity of the crack front, thus enabling us (for the first time) to directly measure those deformations inside the concrete specimen. A detailed discussion of the experimental technique is first provided. Then, following the experimental measurements, test results are presented and discussed. Preliminary results indicate that there is a narrow zone on each side of the crack front with inelastic residual strains, and another where strains increase only in the presence of a neighboring crack tip. The width of the process zone is found to be about three times the maximum aggregate size.