In today’s rapidly evolving world of technology, the need to modernize legacy software systems has never been more pressing. Organizations across different industries are struggling with challenges caused by outdated software. Legacy systems can often hinder innovation, reduce efficiency, and hide potential risks of failure. Modernization gives organizations the ability to prevent these difficulties and enhance organizational competitiveness, and adaptability in the ever-changing business environment. Modernization is a critical yet complex undertaking for any organization. It involves numerous factors that must be carefully considered and evaluated, as they significantly influence the direction and success of the modernization effort. To ensure taking wellinformed decisions about the most appropriate activities and approaches for modernization, it is crucial to have a collection of relevant factors and to consider their current state. Different stakeholder perspectives carry with them different factors and can change the way a factor is perceived and prioritized. One of the significant challenges in modernization is the interdependence of these factors. Many of them can be influenced by other factors or, conversely, they could affect others. This interconnectedness increases the complexity of the decision-making process, which in turn requires additional observation of the factor’s relations. Therefore, it is crucial to have a summarized overview of the influences between the factors as a foundation for understanding. While existing literature provides valuable insights into specific aspects of modernization, it often falls short of offering a holistic view that encompasses the intricate interplay of technical, financial, organizational, and strategic factors in the decision-making process. This thesis aims to address this gap by conducting a Systematic Literature Review to investigate existing research on software modernization and collect information about the relevant factors and their influences. The goal of the study is to create a conceptual model that not only gathers the relevant factors for modernization decisionmaking but also illustrates their complex relationships. It also aims to incorporate the diverse perspectives of business and technical stakeholders, acknowledging that the overview of the factors involved in the modernization decision making will differ based on the viewpoint adopted. Ultimately, the study seeks to identify, gather, and address critical factors, in order to prevent the oversight of any important elements that could negatively impact the modernization process. Additionally, it aims to reveal the complex nature of modernization by offering a clear visual representation of the relevant factors, their definitions, and interrelations, aiming to facilitate better communication and decision-making among stakeholders.