Most natural and technological flows are turbulent, i.e., the flow is irregular or erratic, and difficult to describe, let aside to predict. Turbulent flows are characterized by much faster transport (mass, momentum, and heat) than molecular transport alone. This can be exploited, e.g., to enhance mixing, but quite often, it is desired to be suppressed, e.g., to reduce turbulent drag, all of which cannot be achieved without understanding the physics of turbulence, especially high-Reynolds-number turbulence. Many turbulent flows also involve more physical mechanisms, rather than just mechanically-driven flow of a "pure" fluid. For example, there might be a dispersed phase in the fluid, such as clouds, sand storms, fuel sprays, etc. For these multi-phase flows, the key issue is the interaction between the dispersed "particles" with turbulence. In turbulent combustion, the heat release by combustion influences the flow, while on the other hand, the turbulence affects the flame as well by stretching and rotating it, and by changing the transport of chemicals in the process. A complete understanding of turbulent combustion can only come after the understanding of combustion-turbulence interaction.