Multi-criteria decision-making (MCDM) is a complex process that evaluates and prioritizes options based on multiple criteria, often involving conflicting objectives. In energy efficiency projects, MCDM can be applied to balance cost, environmental impact, and energy savings, enabling more informed and sustainable choices. For portfolio optimization, it assists in selecting a mix of projects that maximize returns while managing risk and resource constraints. Essential for implementing MCDM are digital tools like data analytics and decision support systems.

The paper's theoretical framework examines the relationship between project portfolio optimization and MCDM, enabling a comprehensive project evaluation based on cost, risk, environmental impact, and energy efficiency. This approach is particularly appropriate for energy efficiency projects with specific requirements such as sustainability, long-term cost savings, and compliance with environmental regulations. Digital tools facilitate this process by providing advanced data analytics and decision support, which is crucial for
balancing these complex, often conflicting criteria. This synergy between portfolio optimization and MCDM, especially in energy efficiency, emphasizes the theoretical model's practical relevance and applicability.

In the empirical section of the study, we test our theoretical considerations by analyzing case studies from platforms like SCOPUS. These cases can provide concrete evidence of how MCDM, coupled with digital tools, effectively optimizes project portfolios, especially in energy efficiency projects. The analysis of diverse real-world scenarios demonstrates the practical effectiveness of MCDM in meeting specific project requirements and realizing strategic portfolio goals.

In conclusion, this paper aims to bridge the theoretical and empirical realms, demonstrating the effectiveness of MCDM in project portfolio optimization, particularly for energy efficiency projects. The theoretical framework, emphasizing the synergy between MCDM and digital tools, is supported by the empirical evidence from case studies, highlighting MCDM's pivotal role in guiding strategic decisions and optimizing portfolios to meet both efficiency and sustainability goals.