The rheological characterisation of sludges can be broken down into three steps: viscometry, rheological modelling and correlation of parameters. Viscometry can be performed in either rotational or tube instruments, but the tube instrument is preferred. Data analysis techniques are described and problem areas highlighted. Rheological modelling of sludges has been done traditionally using the pseudoplastic or Bingham plastic models. It is shown that the use of the yield pseudoplastic model provides a more accurate basis for further analysis and a pumped pipeline example is presented as illustration. The correlation of rheological parameters against concentration using a priori methods is discussed and illustrated using a sludge example.