ERP systems are now offered on the cloud under Software as a Service (SaaS) model. For Small and Medium sized Enterprises (SMEs), this is considered the best opportunity to take advantage of the capabilities of an Enterprise Resource Planning (ERP) system without the investment and management costs associated with the on-premise model. This paper investigates the factors influencing the adoption of SaaS ERP system by SMEs. Using a cross-sectional field study conducted across four major case study organizations and software vendors, this paper identifies the determinants for the adoption decision and analyses benefits and challenges.