The efficiency of travelling-wave tubes (TWTs) operated under nonlinear conditions is usually enhanced by adjusting the phase velocity of the slow-wave circuit towards the output end of the tube. This technique, known as tapering, aims to maintain the optimum phase relationship between the electron bunches and the slow electromagnetic wave. The paper describes the results of a study of taper design carried out using a one-dimensional large signal computer model of coupled-cavity TWTs. An improved taper design procedure for broad-band TWTs is suggested.