An angle sensor, system and method employ a guided-mode resonance. The angle sensor includes a guided-mode resonance (GMR) grating and a resonance processor. The resonance processor determines an angle of incidence of a signal incident on the GMR grating. The resonance processor uses a guided-mode resonance response of the GMR grating to the signal to determine the angle of incidence. The angle sensing system includes the GMR grating, the resonance processor and further includes an optical source that produces the signal. The method includes providing a GMR grating, detecting a guided-mode resonance produced in the GMR grating when subjected to an incident signal, and determining an angle of incidence of the incident signal from one or both of a number of and a spectral distance between guided-mode resonances present in a response of the GMR grating to the incident signal.