an apparatus and method for in situ monitoring the viscosity and cure of resins using viscosity dependent fluorescence uses a fiber optic waveguide to introduce light to the resin of a wavelength exciting fluorescence and to conduct the emitted light to a monitor . the emitted light parameters correlate to the viscosity and cure conditions of the resin . the apparatus and method may be used to control composite construction and to provide information on the in service condition of composites .