This study investigates critical success factors (CSF) in implementing Enterprise Resource Planning (ERP) systems. It reviews 94 such factors discussed in journals, conference proceedings and books, published for the most part in the last decade, covering the full lifecycle of ERP systems. Questionnaires exploring these 94 factors were submitted to hundreds of respondents, divided into five groups. The authors of the study hypothesize that the 94 success factors can be grouped, in overall and in each phase of ERP life cycle, under several extracted construct emerged from a statistical extraction method accompanied by business logic coming up with a term that best describes the content domain of the attributes that weight highly on relevant construct. This study presents an examination process of validity, principal component, similarity, reliability and multicollinearity analyses for hierarchical formations of success factors for the entire ERP life cycle and for each one of the six ERP life cycle phases (planning, implementation, stabilization, backlog, new module and major upgrade). This research exhibits for each ERP life cycle phase the main sub factors that explain the main themes of ERP implementation for the most. Special attention is given to: (a) earlier research on CSFs for ERP implementations, (b) hierarchical formation of parent and sub-factors in overall and in each phase of ERP life cycle and (c) representative meanings of critical