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In this letter, a multistage group detection (MSGD) approach to nonlinear equalization is proposed. At each stage, symbols are divided into groups, and maximum-likelihood detection (MLD) within the group is performed. The MLD process identifies a number of promising group values. It is constrained to only consider candidate symbol values identified in the previous stage. Groups are formed by combining groups from the previous stage. For example, symbols are detected one at a time, then two at a time, then four at a time, and so on. The last stage is a form of constrained maximum-likelihood sequence detection (MLSD). The overall demodulation process can be viewed as approximate MLSD, and results show that near-MLSD performance is possible with reasonable complexity. While the High Speed Downlink Packet Access (HSDPA) cellular system is used as an example, the approach can be applied other situations, including the Long Term Evolution (LTE) uplink and MIMO.