Zooplankton is defined as drifting ecologically important organisms that are an integral component of the food chain and also evaluate the ecological status of water bodies. Ecologically zooplankton are one of the most important biotic components influencing all the functional aspects of an aquatic ecosystem such as food chains, food webs, energy flow and cycling of matter. Zooplankton population is very useful indicator for biological, physical and chemical process of aquatic system because they are strongly affected by environmental conditions and respond quickly to changes in water quality. The most important types of zooplankton include the radiolarians, foraminiferans, dino flagellates, cnidarians, crustaceans (including larvae), molluscs, echinoderm larvae and chordates. Zooplankton are the intermediate link between phytoplankton and fish. Hence, diversity and seasonal variation studies of zooplankton are of great importance in water bodies. The present paper deals with the review of available published literature during the present century and that cover the above mention areas of zooplankton biology. The literature reviewed clearly suggests us to conclude that in spite of such a voluminous work done by many scientists, still there are some gaps in terms of geographical or biological aspects. Considering Rajasthan, and Hadoti region specifically, many river systems need extensive study and it may be safely expected to find out some new genera species and this information can be utilized to solve food scarcity problem in the world.