In the 1970s regional groundwater modelling began to be used in support of many hydrogeological investigations in the UK. A number of the studies were concerned with groundwater development at a regional scale in conjunctive use schemes; elsewhere the effect of pumping from aquifers on river flows or the ingress of saline water was considered. Due to the limited power of digital computers at that time, special numerical codes were often prepared for individual projects, with consequent inefficiency and inconsistency of practice. However, by the mid 1990s the need to formalize and standardize groundwater modelling projects was recognized. The Environment Agency of England and Wales prepared a strategy to manage and monitor the projects. A Template Project Brief was prepared to define the many tasks involved in groundwater studies and to clarify the roles of contractor and client (Environment Agency). In addition Guidance Notes were prepared to disseminate procedures and techniques that had resulted in successful outcomes. This paper summarizes some of the earlier studies, provides information about the Project Brief and Guidance Notes and illustrates some critical issues in groundwater modelling by reference to two case studies.