During the last two decades, many tomographic reconstructors have been proposed in the AO literature and some have been implemented on sky on existing MCAO systems. This paper presents an overview of MCAO reconstructors. Four categories of reconstructors are considered: i) the reconstructors based on interaction matrix; ii) the minimum-variance static reconstructors; iii) the 3-step recontructors and iv) the Kalman-based reconstructors. We discuss their relative advantages and drawbacks.