Advanced numerical modeling for carbon steel members (including cold-formed steel members and hot-formed steel members), from manufacturing to the structural response under the applied loading, requires the knowledge of the stress-strain relationship of the material over the full range of tensile strains. Although there are some existing stress-strain models available for carbon steels, they are either only capable of accurate predictions over a limited strain range or defined by many material parameters and the values of some of these material parameters are not available in most of the existing design codes. Therefore, new stress-strain relationships of carbon steels up to the ultimate strength are required for the advanced numerical modeling and need to be expressed in terms of three basic material parameters (the so-called Ramberg-Osgood parameters: the 0.2% proof stress  0.2 , the initial elastic modulus E0 and the strain-hardening exponent n ). This thesis is concerned with new stress-strain models for light gauge carbon steels. In the present study, the stress-strain data obtained from tensile coupon tests reported in existing literature have been collected and analyzed. These tension coupons were cut from virgin steel sheets, cold-formed light gauge steel sections and hot-formed steel sections. Cold-formed light gauge steels possess nonlinear stress-strain curves of round-house type. Hot-formed steel sections and some grades of thin steel sheets possess stress-strain curves with a yield plateau. In this study, the collected experimental data are classified into three different types of steels: (1) cold-formed light gauge steels, (2) all light gauge carbon steel grades (hereinafter simply referred to as “all carbon steel grades”, which includes both cold-formed steels and hot-formed steels), and (3) light gauge carbon steels with a yield plateau prior to strain hardening ii (hereinafter simply referred to as “carbon steels with a yield plateau”). The thesis presents new stress-strain models for these three types of carbon steels, which have been developed by a careful interpretation of existing experimental data. These new models are capable to describe the stress-strain relationship of light gauge carbon steels over the full range of tensile strains by using only three basic Ramberg-Osgood parameters (  0.2 , E0 and n ). The accuracy of these proposed models has been demonstrated by comparing their predictions with experimental stress-strain curves. Comparisons clearly demonstrate the advantage of the proposed models over the existing full-range stress-strain models. In addition, the effect of the strain rate used in tensile tests on measured stress-strain curves has also been investigated and discussed