Knowledge retention (k-retention) is vital for various enterprise resource planning (ERP) implementations in Small and Medium-sized Enterprises (SMEs), though it is a highly demanding and challenging task. The aim of this paper is to investigate different types of approaches to k-retention and factors influencing k-retention in SMEs. Our study adopts a grounded theory approach with cases based on 12 ERP implementations in UK SMEs. We analyse our data using thematic analysis. The findings reveal specific elements that support the k-retention of ERP package knowledge and business process knowledge. These elements are; k-retention tools, documentation, human capital, and the understanding of k-retention challenges. In addition to insights from these aspects, our study reveals two additional factors (project management and organisational culture) that influence ERP package k-retention and business process k-retention. Based on these findings, we develop an ERP k-retention (EKR) framework that can be utilised by SMEs which are considering implementing ERP systems, to facilitate knowledge retention during implementation.