Formal (mathematical) methods are being increasingly used in the development of software systems. It is recognized that formal specification of a problem, before attempting to write a program, can lead to a more accurate solution. A number of industrial trials and case studies have demonstrated the benefits of a number of formal methodologies. It is apparent also that acceptance and use of such methods will be greatly aided by the development of software tools to manipulate the notation involved. The authors describe a tool set developed to assist the construction of specifications using the Vienna Development Method (VDM). A certain familiarity with VDM is assumed, and only a brief resume is given.