This thesis develops and validates a decision support system (DSS) to support Project stakeholders in the selection of the most suitable project management methodology, between Traditional, Agile, or Hybrid, for international IT projects in Europe.

The DSS is built on a structured identification and weighting of Critical Success Factors (CSFs) that influence methodology selection. Although the broader literature lists many CSFs for IT project success, only 59 were identified as having a conceptual link to a methodology selection. Through iterative refinement based on ten expert interviews and a survey, 26 weighted decision factors are selected. The DSS is supported by an Excel-based tool that applies a 100-500 scoring range, category-level weighting, and grey-zone confidence logic to generate context-specific methodology recommendations.

Empirical Validation demonstrates a current 92% accuracy rate, highlighting the robustness and practical relevance of the model. The DSS addresses key gaps in existing frameworks by supporting hybrid approaches, enabling context adaptation, and offering a traceable, practitioner-oriented decision process. The study contributes to theory and practice by providing a validated and evidence-based model for methodology selection in complex, cross-border IT projects.