This chapter deals with the study of parallel/cross feed flow multiple-effect evaporator (MEE). The performance of MEE is strongly dependent on the feed configuration. Generally MEE is classified in four types based on feed flow: forward feed, backward feed, parallel feed, and parallel/cross feed. Generally in the parallel/cross feed configuration, feed seawater enters each effect of the MEE with equal or almost equal flow rates. In a thermo-vapor compressor (TVC), low-pressure vapor extracted from the MEE is compressed with a high-pressure motive steam to produce medium-pressure vapor. Similarly for an MEE-TVC system, the feed flow rate for an effect operating at a higher temperature increases, and the cooling duty requirement decreases. The methodology is based on the principles of process integration and mathematical optimization. The MEE generally requires low temperature heating, and are often integrated with power plants, a waste heat source, or a sensible heating source.