The presentation will review the physical mechanisms governing the impact dynamics of droplets and jets. We shall first discuss the essential components of such impacts by considering the reference case of the head-on collision of two identical droplets, emphasizing the roles of droplet deformation, the internal motion generated and the associated viscous loss, the rarefied nature of the gas flow in the interfacial region, and the van der Waals force that effects surface merging such that, with increasing impact inertia and depending on the rheological properties of the liquid, the colliding droplets could exhibit the non-monotonic outcomes of merging, bouncing, merging again, and merging followed by further separation with the concomitant production of secondary and tertiary droplets. We shall then discuss the impact dynamics in four related phenomena, namely: (1) the collision between two unequal sized droplets, focusing on the generation of internal jets upon merging and the associated mixing efficiency; (2) the collision between droplets of non-Newtonian fluids that are either thinning or thickening; (3) the collision of two identical jets exhibiting the same four regimes of merging versus bouncing as those of the droplets; (4) droplet impact onto a thin film, the resulting merging versus bouncing responses, and the experimental observation of the evolution of the thin interfacial gas film. Directions for further research are suggested.