Grafting, in the context of polymer chemistry, refers to the addition of polymer chains onto a surface. In the so-called grafting onto mechanism, a polymer chain adsorbs onto a surface out of solution. In the more extensive grafting from mechanism, a polymer chain is initiated and propagated at the surface. Because pre-polymerized chains used in the grafting onto method have a thermodynamically favored conformation in solution (an equilibrium hydrodynamic volume), their adsorption density is self-limiting. The radius of gyration of the polymer therefore is the limiting factor in the number of polymer chains that can reach the surface and adhere.  The grafting from technique circumvents this phenomenon and allows for greater grafting densities.
The processes of grafting "onto", "from", and "through" are all different ways to alter the chemical reactivity of the surface they attach with.  Grafting onto allows a preformed polymer, generally in a "mushroom regime", to adhere to the surface of either a droplet or bead in solution.  Due to the larger volume of the coiled polymer and the steric hindrance this causes, the grafting density is lower for onto in comparison to grafting from. The surface of the bead is wetted by the polymer and the interaction in the solution caused the polymer to become more flexible.  The extended conformation of the polymer grafted, or polymerized, from the surface of the bead means that the monomer must be in the solution and there for lyophilic. This results with a polymer that has favorable interactions with the solution, allowing the polymer to form more linearly.  Grafting from therefore has a higher grafting density since there are more access to chain ends.
Peptide synthesis can provide one example of a grafting from synthetic process. In this process, an amino acid chain is grown by a series of condensation reaction from a polymer bead surface. This grafting technique allows for excellent control over the peptide composition as the bonded chain can be washed without desorption from the polymer.
Polymeric coatings are another area of applied grafting techniques. In the formulation of water-borne paint, latex particles are often surface modified to control particle dispersion and thus coating characteristics such as viscosity, film formation, and environmental stability (UV exposure and temperature variations).