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At or near atmospheric pressure, overvolted gas breakdown results in a streamer formation. In many applications of non-thermal plasma where efficient excited species generation is critical, the streamers are quenched to prevent it from reaching the arc phase. This can be achieved by repetitive nano second pulsing or dielectric barrier discharges were the dielectric charging quenches the arc formation. In such discharges, the plasma characteristics such as electron and ion densities and the production of excited species is determined by the streamer properties. Over the past five decades, a vast amount of experimental and computational work has been accumulated to establish a well-accepted theory of streamer formation and propagation. In this article we discuss the fluid models for streamers and quantify some macroscopic properties which can inform specific applications. We discuss in detail the fluid equations needed to model streamers and several schemes of parametrization of the transport and electron collisional processes. From an application point of view, the steamer simulations are used to quantify the excited species production by electron impact. This information is used to predict the specific outcomes via the plasma chemical conversion pathways. We present results of streamer discharges for three applications which are of technological importance to illustrate this approach: Plasma-assisted combustion, remediation of toxic gases, and plasma medicine. For plasma-assisted combustion the results of hydrogen ignition are discussed since non-hydrocarbon-based fuels such as hydrogen and ammonia are potential fuel candidates to reduce greenhouse gases. For the remediation of toxic gases, we discuss the removal of SOX/NOx from flue gas. Plasma medicine is a relatively new field and repetitive nano-second pulsed discharges in a helium gas carrier shows promise as a reactive plasma source for treating biological material. We discuss the helium metastable production in a streamer discharge since this species leads to the production of OH radicals which plays an important role.