An industrial perspective on modelling software is presented that highlights the key requirements of process system engineers. This includes a description of the actual modelling activity itself and emphasises the complex inter-relationships and knowledge involved. An advanced modelling environment is described which incorporates state representations of process entities, the mathematical relations that associate them, and the activities used to manipulate them. It is argued that this environment is the first capable of fully capturing the knowledge and relationships required adequately to represent modelling activities. Adoption of similar techniques to those presented here will be a necessary step forward if flexible, large scale integration of modelling techniques, development tools, methodologies and domain expertise is to be achieved within a single usable system.