Based on the steady state and the transient solutions of the phenomenological theory of sedimentation, a software was developed for the design and simulation of batch and continuous thickening. The paper presents a brief description of the phenomenological theory of sedimentation and its application to batch and continuous thickening with two appropriate initial and boundary conditions. The software permits the simulation of batch sedimentation and the design and simulation of continuous thickeners. For batch thickening, the initial and critical concentration and the height of the initial suspension have to be entered together with the parameters of the flux density function and the effective solid stress. The output is a settling plot showing as many lines of constant concentration as requested and a plot of the concentration profile for several times. For continuous thickening, the program calculates the unit area and the area of a thickener required to treat a given feed rate. The input is the solid feed rate and the required underflow concentration, together with the thickening parameters. One example shows the application. (C) 2002 Elsevier Science Ltd. All rights reserved.