The compositional and microstructural evolution of different generations of γ’ precipitates during the continuous cooling, followed by isothermal aging, of a commercial nickel base superalloy, Rene 88DT, have been characterized by three dimensional atom probe tomography (3DAP) coupled with energy-filtered transmission electron microscopy (EFTEM) studies. After solutionizing in the single γ phase field, during continuous cooling at a relatively slow rate (~ 24°C/min), the first generation primary γ’ precipitates, forming at relatively higher temperatures, exhibit near-equilibrium compositions, while the smaller scale secondary γ’ precipitates, forming at lower temperatures, exhibit non-equilibrium compositions often consisting of excess Co and Cr, while being depleted in Al and Ti content. The compositions of the γ matrix near these precipitates also exhibit similar trends with the composition being closer to equilibrium near the primary precipitates as compared to the secondary precipitates. Subsequent isothermal aging at 760°C, leads to some coarsening of the primary γ’ precipitates, but does not affect their composition significantly. In contrast, the composition of the secondary γ’ precipitates is driven towards equilibrium during the isothermal aging.