This chapter is primarily intended as an introductory text, a pedagogical platform, on the phenomenon of turbulence in fluids. For the sake of simplicity, the discussion is mostly limited to the case of an incompressible (constant-property) newtonian fluid in simple three-dimensional turbulent flows. Additional complexities related to thermal convection, magnetic forces, nuclear reactions and so forth are ignored on purpose. The main motivation is to exhibit the general problematic of turbulence in an as simple as possible physical setting. Modelling prospecting, which aims at elaborating numerically tractable mathematical models of turbulence, is also brought up.