This paper presents an overview of the posters presented in sessions 7 and 8 of the Watermatex 2000 conference. These posters present two aspects of modelling biological processes--model selection and calibration. Special attention is given to the papers on OED (Optimal Experimental Design), which is a method of optimising the data collection for model selection and calibration. The presence of these presentations at the conference highlights the continuing significance of modelling and stresses the requirement of improvements in modelling techniques. The papers provide some contribution to this end.