"Definite" is a decision support software package that improves the quality of environmental decision making since it: structures the decision process; makes full use of available information; provides a rational, responsible and justifiable decision that is open for external review; and allows the exploration of all the options by the use of 'what if?' scenarios. "Definite" is, in fact, a whole toolkit of methods that can be used on a wide variety of problems. If there is a problem to be solved and alternative solutions can be identified, then "Definite" can weigh up the alternatives and assess the most reasonable option. The system contains a number of methods for supporting problem definition as well as graphical and other methods to support representation. In the assessment of the problem, "Definite" can support priority allocation in a number of ways. "Definite" can deal with all types of alternatives, thanks to the inclusion of five different multicriteria methods, as well as cost-benefit and cost-effectiveness analysis. Related procedures such as weight assessment, standardization, discounting, and a wide variety of methods for sensitivity analysis are also available. "Definite" - allowing for fifty alternatives and fifty effects - supports the whole decision process, from problem definition to report generation. The structured approach adopted ensures that the decisions arrived at are systematic and consistent. The full version of "Definite" comprises: the book, "Multiobjective Decision Support for Environmental Management"; "The Definite User Manual"; the Definite software package; and a helpdesk for user support.