The study focuses on the crack initiation mechanisms in dwell fatigue of alloy 718. Fatigue, dwell fatigue and creep tests were performed at 610°C. All tests were stress-controlled at a positive stress ratio. Depending on the hold time, some similarities were identified between dwell fatigue tests and creep and fatigue tests through accumulated plastic strain and fracture surfaces. In an aim to rule out any contribution of oxidation to damage development, vacuum tests were performed. Interrupted tests were also carried-out with a view to understanding the development of damage mechanisms. Interactions between creep mechanisms identified as grain boundary sliding and environment were obtained for long hold times. These tests also suggest that crack initiation mechanisms originate from an interaction between plastic strain localization at grain boundaries and environment.