What is meant by “soft condensed matter?” In the context of this NATO Advanced Study Institute, soft systems are those where the relevant interactions are weak and thermal fluctuations play an important role. However, this is not a sufficiently sharp definition because all materials that have higher order or weakly first order phase transitions, e.g., magnetic materials, superconductors, etc., have this property. I believe that “softness,” in addition, implies a relatively high bulk or osmotic compressibility. For a system with a transition temperature, TC, the elastic modulus, G, scales as $$G = {T_c}{L^{ - 3}}$$ (I.1) where L is the characteristic spatial scale which is typically the size of the relevant building blocks (not too near a second order phase transition). Thus, softness suggests L ≫ a, where a is an atomic dimension. With this in mind, we are led to the consideration of correlated systems composed of superatomic objects. These may be fluids (vanishing static shear modulus, or weak solids, e.g., colloidal crystals, ordered micellar phases, etc. For the most part, then, this Advanced Study Institute will focus on the physics of complex fluids, where the complexity is associated with the multiple energy scales required to adequately describe the systems. In this introductory lecture, I will attempt to set the stage by reviewing the fundamental interactions which control the ultimate physical properties.