Abstract: Prior studies have shown that many reinforced concrete buildings located in seismically active regions do not have the necessary lateral strength and ductility to perform adequately in earthquakes. In particular, it has been noted that reinforced concrete columns with poor transverse reinforcement are susceptible to shear failure and loss of axial capacity under cyclic lateral loads. The research reported here is focused on modeling the lateral deformation behavior of lightly reinforced concrete columns subjected to lateral loads. Lateral deformations in a column are comprised of three parts: flexural, reinforcement slip, and shear deformations. The monotonic response for each of these deformations was modeled separately. Flexural deformations were modeled using moment-curvature analysis and a plastic hinge model. A review of existing models for reinforcement slip was completed, and an existing model was modified based on experimental data and a parametric study. A comparison of models showed that the proposed slip model performs well in terms of accuracy and efficiency. A shear model was adopted from a previous study, and combined with an available computer program to predict shear behavior in this study. These three component models were found to predict the lateral response envelopes acceptably well for several sets of experimental data. A model for the overall lateral force-deformation relationship of reinforced concrete columns was created by combining the effects of each of the component models. The behavior of a column is classified into one of five categories based on a comparison of the shear, yield, and flexural strengths. The expected behavior in each category determines rules that govern the combination of the deformation components. For columns that are susceptible to shear failure after the onset of flexural failure, the response envelope is modified based on an available shear capacity model. An axial capacity model is also employed for the prediction of ultimate deformations. The proposed model was compared with experimental data from 37 column tests by various researchers. It was found that the classification system employed in the model was successful in representing column behavior. Overall, the model did a reasonable job of predicting the lateral response envelope for the columns in the test database. The model predicted the peak lateral strength well, and successfully represented the onset of shear failure in columns initially failing in flexure.