Enterprise Resource Planning Systems (ERP) have become the de facto management information systems standard during the decade for major corporations and are expected to recognize significant gains in the Small and Middle-sized Enterprises (SME) market segment.  ERP implementations are now beginning their “Third Wave” in large-scale corporations, but contrastingly, only beginning to penetrate the SME market.  This study specifically addressed the Critical Success Factors (CSF) in large-scale installations established by Somers and Nelson, subsequently condensed by Loh and Koh, and compared them to similar SME findings.  The findings are presented utilizing the Cooper and Zmud structured process theory model establishing CSFs relative to an ERP implementation life cycle model.