Experimental results have shown that the plastic flow resistance of as-built additively manufactured stainless steel materials (304L and 316L) from the laser engineered net shaping (LENS) process is substantially greater than that of additively produced and annealed and traditional wrought and annealed materials. The structure of these as-built materials is also substantially different than traditionally produced polycrystalline metallic materials. Since the additive process builds the component from successive deposition of laser melted beads – similar to welding – the structure of the material has two characteristic lengths. The first is the dimension of the bead, with interbead topologies subject to the laydown pattern required by the component and secondly the grain structure within each bead. The grain structure within the bead is topologically complex and subject to change based upon process conditions. In the examination of the as-built material, there are a number of physical factors which could contribute to this difference in plastic flow response – grain size, grain morphology, initial dislocation state, internal stress, chemical composition, and laydown bead structure. In addition, dynamic experimental results suggest that inter-bead interfaces, play a key role in the general mechanical behavior of additively manufactured material. Two-dimensional metallographic analysis has been carried out on three different 316L materials – as-built additively manufactured, heat treated additive, and wrought. These results show that grain size and morphology of the additive material is substantially different than the other two materials. The literature suggests that grain size and its influence on flow stress is reasonably strong for these stainless steel materials. We employ a model for the single crystal response of these stainless steel alloys which is dependent upon dislocation density and takes into account a tensorial representation of dislocation interactions within a large deformation framework. We also represent the grain size effect within this local model with a simple “Hall-Petch” addition to the flow stress which to first order is able to represent the complex structure of the material. Diffraction experiments on these materials quantifies the initial dislocation density state of the three materials and is used in the context of this single crystal model to properly initialize the three material states. Polycrystal simulations of these three different material structures are performed and comparisons made against available experimental information to diagnose the physical reasons for such large differences in flow stress and structural performance. These results will be discussed in the context of the LENS process and remaining challenges to the theoretical description of this new class of material in the future.