Cyclic near-tip stress fields which evolve ahead of fatigue cracks are known to have a pronounced effect on the fracture response of materials. This region of reversed damage is responsible for the initiation of fatigue cracks from stress concentrations under fully compressive cyclic loads, crack growth retardation following tensile overloads, and transient crack growth response under spectrum fatigue loading. By recourse to photoelasticity and laser interferometry, we provide direct and in situ measurements of cyclic near-tip stresses ahead of notches and fatigue cracks in amorphous polymers subjected to cyclic tension loading. The near-tip stresses are quantified during both the loading and unloading phases of the fatigue cycle, as well as during various stages of crack advance, in an attempt to establish a link between the evolution of near-tip stress fields and the advance of the fatigue crack. In addition, transmission electron microscopy analyses of the near-tip region have been performed to characterize cyclic deformation mechanisms.