This thesis presents a comprehensive experimental and theoretical investigation carried out to study the behaviour and to determine the ultimate compressive strength, f¹_m, of blockwork masonry prisms. The enhancing effect of strain gradient on f¹_m caused by eccentricity was studied using two different eccentricities. The thesis also presents the results of an experimental and theoretical investigation carried out to study the strength and behaviour of reinforced blockwork masonry built with different percentages of vertical reinforcement and subjected to different eccentricities in order to establish the load-moment strength interaction diagrams. On the basis of the test results gathered from the experimental part of this study and the basic assumptions used in the design of reinforced concrete columns using ultimate limit state principles, a theoretical method was suggested to predict the ultimate strength of reinforced blockwork masonry columns subjected to axial and eccentric loads.