Supplier selection is one of the vital processes which have an impact on the competitiveness of firms by affecting their costs, the quality of goods and services produced, and customer satisfaction. Suppliers'' evaluation is a multi criteria decision problem associated with several perspectives such as cost, quality, logistics, production, finance and sales. This necessitates the involvement of different parties within a firm and requires a group of decision makers to work collaboratively to come up with an acceptable solution. Additionally, the evaluations should be repeated regularly and the decision process should be as short as possible to be responsive in a competitive environment. In this work, a web-based group decision support system (GDSS) is developed to solve the supplier selection problem by using an AHP model. The GDSS provides a flexible and dynamic environment which enables the participation of several parties with the use of advanced web technologies to cope with the complexities of the supplier selection problem. This book is of interest for those who are involved in decision making processes of evaluation problems and those who are interested in developing a GDSS.