Title: Critical Success Factors for Integration of Enterprise Resource Planning System   Level: Student thesis, final assignment for Master Degree (one year) in Business Administration   Author: Kambiz Kafi   Supervisor: Dr. Maria Fregidou-Malama   Examiner: Dr. Ehsanul Huda Chowdhury   Date: 2018-11-26   Aim: This study examines the Critical Success Factor (CSF) model and its implementation in a case study where ERP Systems are integrated. The model includes Legacy System as a CSF.   Method: Deductive reasoning and case study were applied to support the research theory. Primary and secondary data were collected. Interviews with managers and staffs were performed.   Result & Conclusions: The study shows the factors that are critical in successful implementation of ERP project and how a successful implementation and integration of ERP projects is executed when two companies are being merged. It also shows how the ERP integration project can be implemented. This work studied an implementation of Holland and Light’s theoretical CSF model empirically and validated that the model is general and robust for successful ERP implementation and managing changes.   Contribution of the research: This study of integration of few Legacy Systems when companies are being merged is a contribution to the theory of CSF. The central role that Legacy Systems plays in ERP project implementation is shown empirically. This study presents Software Alignment (Software Configuration) based on two company’s business processes empirically and found it to be essential in success of ERP projects. The research shows how CSF model manages changes, assisting managers in merging two companies successfully. The research presents a modified Holland and Light CSF model to meet the merging situations.      Suggestions for future research: To gain more knowledge about CSFs for integration of ERPs, this study suggests further cross- industrial empirical studies in wholesale and retail industries with varied sizes. Research about identifying CFSs in extended ERP using e_CRM is recommended.