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Near-threshold fatigue crack propagation behavior of metallic alloys has been widelystudied and documented during the last three decades. Several factors or parametershave been shown to play a major role [1,2,3]. Firstly, the microstructure effects havebeen shown to dominate the near-threshold regime and to widely influence the crackpath. Secondly, comparative measurements of fatigue crack propagation rates in air andin high vacuum have demonstrated the existence of a detrimental effect of atmosphereenvironment for most of the metallic materials fatigued at room temperature this effectbeing much more accentuated in the near-threshold area; experiments conducted undercontrolled partial pressures of water vapor have clearly related the acceleration of thefatigue crack growth rate to the presence of moisture in the surrounding gaseousenvironment [4]. Thirdly, crack closure in the near-threshold area induces enhancedshielding effects which depend on the crack wake and hence on the crack path(plasticity, closure mismatch of rough surfaces, oxidation) [5].This paper deals with a review on the role of microstructure and environment on thenear-threshold fatigue crack propagation behavior in Aluminum alloys and particularlyon Al-Zn-Mg alloys. Possible interactions of crack closure are uncoupled byconsidering data provided by tests with closure correction or without closure. Relationsbetween crack paths and crack growth mechanisms are discussed on the basis ofmicrographic and microfractographic observations.