To prevent disaster in future earthquakes, the existing deficient buildings need to be retrofitted. One way of retrofitting the columns in reinforced concrete multi-storeyed buildings is concrete jacketing. The present study investigated the effect of jacketing on the flexural strength and performance of columns. First, slant shear tests were conducted to study the interface between old and new concrete. Second, column specimens were tested to study the strength. Third, beam−column−joint sub-assemblage specimens were tested to study the ductility (energy absorption) and energy dissipation. Analytical investigations were carried out to predict the experimental results. A lamellar approach and a simplified method of analysis were used for the prediction of the axial load versus moment interaction curves and moment versus curvature curves for the retrofitted columns. An incremental nonlinear analysis was adopted to predict the lateral load versus displacement behaviour for a retrofitted sub-assemblage specimen. Guidelines for retrofitting of columns by concrete jacketing are provided.