Rapid development of information technology and communication (ICT) has increased the use of information systems in organizations since a decade ago. At the same time, many organizations are still using old information systems to support their business, known as legacy systems. Even though these systems cause technical problems, but they are still used to support service delivery to the customer. These systems are also essential to organizations as they have been operated for many years and possess high business value. The operation of legacy systems cannot be stopped quickly, as it will affect daily business tasks. However, organizations with legacy systems need to think about the ability of the systems to support their future direction. Modernization of legacy systems needs to be implemented to ensure the systems are aligned with global changes as well as improving the competitiveness of the organizations. This study, therefore, reviewed the phases and factors involved in legacy systems modernization to identify gaps and their insufficiencies. There are many studies on legacy systems, but only a few have focused on the overall process of legacy systems modernization. Most studies on legacy systems are technical in nature and refer to specific aspects and phases of modernization. This study aims to provide overall guidance to the organizations in performing legacy systems modernization.