AbstractFibers and fillers are important raw materials for the preparation of paper products. Similar to fiber engineering, filler engineering for papermaking has become an active research area. There are similarities as well as differences between engineering involving each of these classes of materials. There are differences in such aspects as the nature of materials to be engineered, applicable engineering methods, and engineerablity of the material surfaces. The co-development of fiber engineering and filler engineering can potentially provide many benefits to the papermaking industry. For filler engineering, the relevant research topics broadly can include fibrous filler engineering, hollow/porous filler engineering, acid-stabilization of calcium carbonate fillers, surface encapsulation of naturally occurring polymers or their derivatives, preflocculation, precoagulation, cationic modification, filler/size hybrid formation, organic filler engineering, using combinations of different types of available fillers, multilayer deposition modification, modification with polymer latexes or dispersants, physical modification, mechanical modification, surface functionalization, fines-filler composite/hybrids or fiber-filler composite/ hybrid formation, in-situ polymerization modification, surface grafting, physical treatment in the presence of polymeric additives, filler precipitation, and core-shell composite filler engineering.