Cold-formed steel members are widely used in the construction industry due to their versatility, high strength-to-weight ratio and ease of assembly. Stud columns set in tracks, form the main members in cold-formed steel wall systems, which are typically sheathed with plasterboard or oriented strand board (OSB). The interaction between the cold-formed steel members and the sheathing, which can have a significant effect on the ultimate strength and flexural stiffness due to composite action and bracing, is currently not systematically taken into consideration in design. More than 100 material and connection component tests have been performed to study the behaviour of plasterboard and OSB and their interconnection with cold-formed steel through screws acting in shear and tension. The obtained test results, along with a collected dataset totalling more than 400 physical tests, were used to develop analytical models to describe their load-deformation behaviour; these are suitable for use in numerical simulations and advanced design methods. A total of 17 full-scale sheathed wall stud tests were also performed, with varying connector spacing between either plasterboard or OSB sheathing panels and the steel members. Tests were performed under pure compression, pure bending and combined loading. Reducing the spacing of the connectors from 600 mm to 75 mm resulted in up to 30% increase in capacity while also preventing pull-through connector failure for specimens sheathed with plasterboard. Sophisticated finite element models of wall studs were also developed, which, following successful validation against test results, allowed parametric studies to be undertaken, where the influence of the sheathing, connector spacing and section depth was investigated. Finally, a preliminary design guidance has been developed, where the beneficial effects of bracing, composite action and enhanced boundary conditions at the member ends are recognised, thus enabling more efficient design of sheathed cold-formed steel wall systems.