The construction industry is characterized by highly interdisciplinary, fragmented, and temporary project organizations, process discontinuities, and unique projects (Gustavsson et al., 2012). The processes, activities and operations of construction projects are organized and implemented by different individuals or groups who may have different levels of interest and / or involvement in the project, and they are referred to as project stakeholders (Molwus et al., 2014; Winch, 2010). The lengthy process of designing and executing construction projects constitutes a complex system involving collaboration and negotiation among a number of stakeholders such as investors, designers, contractors, local authorities and various other stakeholders from the project environment (Winch, 2010). This fragmentation makes it difficult to meet the requirements for construction projects in terms of cost, time and productivity (Jahanger et al., 2021; Toor and Ogunlana, 2010). Knowledge of stakeholders and their characteristics in relation to the project is an important step in balancing their (negative) impact on project execution (Cleland and Ireland, 2002). Stakeholders in a construction project are individuals, groups or organizations that affects, are affected, or are perceived to be affected by the decisions, activities or results of the project. In infrastructure construction projects, a large number of contracting parties and the frequent occurrence of conflicting objectives between stakeholders often cause the originally set project objectives to be exceeded (e.g. cost, time...) (Henisz et al., 2012). Therefore, stakeholder engagement (hereinafter AIS) has been recognized as an important strategy for achieving success in construction projects (Molwus et al., 2017). In research that addresses the topic of successful performance of construction projects and the factors that lead to success, only 26% of them are of a quantitative nature (Gunathilaka et al., 2013). Furthermore, research that specifically addresses the topic of AIS in construction projects is most often of a qualitative nature, i.e using interviews and case studies on one or a couple of projects (Hu et al., 2015) where the authors themselves point out the limitations in possible generalization of results As previously mentioned in construction, research on AIS is predominantly of a qualitative nature, rare quantitative research considers successful performance as a single variable and mostly they are not done in the context of construction and infrastructure projects. Consequently, the goals of this research are: 1. The first aim of the paper is to investigate the impact of engagement of stakeholders on the successful performance of infrastructure projects, taking into account different variables for project performance. 2. The second aim of the paper is to develop a framework for the engagement of stakeholders in infrastructure construction projects. Following the defined goals of the paper, three hypotheses of the paper are defined: • H1: Engaging stakeholders in infrastructure construction projects contributes to the achievement of a defined project deadline. • H2: Engaging stakeholders in infrastructure construction projects contributes to the realization of a defined project cost. • H3: Engaging stakeholders in infrastructure construction projects contributes to the achievement of a defined scope and quality of the project 2. Analysis of indicators / criteria for successful performance of construction infrastructure projects The research of Pinto and Slevin (1998), which covered a very large sample of examined projects from a number of industries resulted with newly developed model of projects success. Their model consists of two key sets of criteria: success in terms of project, which includes time, deadline and technical performance, and success in terms of customer (client), which includes use value (usability of project delivery), customer satisfaction and effectiveness (in terms of usefulness and improvement of business opportunities for the client) (Pinto and Slevin, 1998). Many later success models are based on the ideas stipulated in this model. Although in some literature sources, project perfrormance is used as a synonym for the term project success, some researchers emphasize that performance and success are not the same thing (Rajablu et al., 2017). Performance can be measured during and immediately after project completion (Albert et al., 2017; Rajablu et al., 2017; Jha and Iyer, 2007) while from the aforementioned success models (Albert et al., 2017; Turner and Zolin, 2012; Jha and Iyer, 2007; Westerveld, 2003) it is evident that the success of a product and organization is measured only after a certain time lag and they elaborate success as a broad and comprehensive concept. It can be concluded that in addition to the iron triangle or 'cost, time and quality / scope execution', the (soft) indicators of successful performance and 'customer satisfaction' or 'project team satisfaction' were frequent. Project success factors can be defined as elements of a project that can be influenced to increase the likelihood of success and they are independent variables that make success more likely (Gunathilaka et al., 2013). The field of research on success factors is closely related to the topic of success criteria, and.e many researchers consider them as two key areas of research on project success (Davis, 2014; Turner and Zolin, 2012; Westerveld, 2003). Success factors 'project manager competence', 'project participant commitment', 'client competence' and 'project participant coordination' were the dominant factors in terms of improving the level of project execution measured through time (deadline), price and quality (Jha and Iyer, 2007). Such “soft” skills and activities are increasingly aggregated into the discipline of stakeholder management or stakeholder engagement (Project Management Institute, 2013; Westerveld, 2003). 3. Engaging and managing stakeholders in construction projects More and more research in construction management deals with megaprojects or projects of very large volume and complexity, and it is emphasized that for this context the management of stakeholders is extremely important (Hu et al., 2015; Mok et al., 2015) due to the well-known characteristics of large infrastructure ( mega) projects (Flyvbjerg et al., 2009); decision-making, planning and management is the responsibility of several actors; the scope of the project changes over time; they are very complex from various aspects e.g technological, logistical and financial and have a great social impact. Winch’s model (2010) categorizes stakeholders according to pre-defined roles in the construction project, i.e groups and organizations that represent common interests, and the first level is this classification recognizes two classes internal and external stakeholders. The number of stakeholders who are aware of the importance of engagement in the decision-making process is growing and increasingly aware of how important it is to point out each individual request or how important it is to create a working environment that can bring optimal project outcome (Erkul et al., 2020). It can be seen that the involvement of stakeholders is one of the two key aspects of stakeholder management, and PMBOK links three of the four processes to stakeholder engagement, highlighting this as a key aspect. Instrumentalist research that views stakeholder management as a means to an end is detected as the one with the least number of research articles (Yang et al., 2009). A few years ago, a couple of studies emerged that used a quantitative approach and where stakeholder engagement emerged as a (latent) variable, most often independent, and sometimes as a moderator (Khan et al., 2021; Nguyen and Mohamed, 2021; Erkul et al. ., 2020; Molwus et al., 2017; Rajablu et al., 2014, 2017). There are only two empirical studies related to examining the management and engagement of stakeholders in the context of construction projects, one by Molwus et al. (2017) which actually examines the relationship between the perceived importance of stakeholder engagement factors and project success. Another study is from Erkul et al. (2020) that measure the latent variable of stakeholder engagement through unusual manifest variables (e.g. meetings, forums, workshops, interviews...) that are more the use of engagement and communication tools (Khan et al., 2021; Rajablu et al., 2017) rather than activities and processes for stakeholder engagement. 4. Organizing implementation and management in the context of infrastructure construction projects The traditional concept of project management or established management strategies are mostly focused on the technical aspects of the project, and such an approach proves relatively inefficient for modern large and mega projects that have recently become an increasingly common mechanism for critical infrastructure delivery (Li et al., 2019). Luo et al. (2017) state that management approaches must be adapted to today's more complex projects and that in this context certain disciplines are explored such as stakeholder management and procurement models that are forming complex project teams to deliver a construction project. Klakegg et al. (2016) conclude that large public projects are still poorly understood, and that progress is needed in the management of this type of project Stakeholder management (SM) is a separate research area but is often analyzed with the mentioned approaches to creating a project organization which Hu et al. (2015) confirm by placing SM and organizational management as related topics in the literature dealing with complex (mega) projects. In addition to organizational management and stakeholder management, the topic of project procurement and project planning emerges as complementary topics in which there is much room for research progress (Hu et al., 2015) Naoum and Egbu (2015) state that the main goal of procurement is to enable a project that meets its objectives and meets the criteria and expectations of the client and that all definitions of project procurement place emphasis on establishing relationships between internal stakeholders. Winch (2010) argues that the basic principle of construction project management is to mitigate the impact of challenges caused by rigid contractual instruments and the mismatch of project stakeholders. In Croatia, the formal framework of public procurement is regulated by the Public Procurement Act (ZOJN) (NN120 / 16), and the public contracting authorities are mostly state and local government bodies or state companies and agencies. Such contracting authorities mainly have the function of owners for infrastructure projects, and many infrastructure projects in the Republic of Croatia in the last 10 years are (co)financed through grants from EU funds (Central Agency for Financing and Contracting, 2020) On 12 December 2014, the European Commission (EC) approved the Operational Program "Competitiveness and Cohesion 2014-2020", through which the EU has 6.881 billion euros at its disposal. The largest amount of investment, more than 3.5 billion euros, Croatia will invest in environmental protection (water utility infrastructure and waste management), transport infrastructure and adaptation to climate change (defence against floods and other natural disasters) (Central State Portal, 2020). 5. Research methodology The methodology selected in this research can be classified as a mixed methods approach, i.e research approach that uses both qualitative and quantitative research methods. The introductory chapter mentions three hypotheses of this research and two research goals. The research methodology has been tailored in such a way that the application of various scientific methods enables the testing of hypotheses and, ultimately, the achievement of the set research goals. The stages include the entire methodology, i.e all methods related to the definition of variables and measuring instruments, methods related to the collection of qualitative and quantitative data, and finally methods related to the processing of quantitative and qualitative data. 6. Results - Analysis of the Impact of Engaging Stakeholders on the Successful Execution of Infrastructure Projects Data collection was carried out through survey questionnaires. The key research variables are defined on the Likert ordinal scale (which can be approximated into an interval scale), and data analysis is performed in the form of statistical calculations in which the project sample is analyzed using descriptive and inferential statistic. A key part of the chapter is the implementation of the method of structural equation modelling (SEM) by which the research hypotheses were tested. The result of the 1st phase of data collection (through the 1st questionnaire) was obtaining the data on the fifty infrastructure construction projects. In addition to the key information on the project performance (e.g. dependent variable) other relevant information was collected such as information on other project stakeholders which represent the potential respondents for the 2nd part of data collection. All potential respondents for the second project related questionnaire contacted were sent a request to provide the (second) part of the data on the infrastructure project in which they actively participated (the project was named). This resulted in 99 responses for 50 projects in which respondents rated how stakeholder engagement processes were conducted. After the latent variables have been roughly defined in the previous steps, the PLS-SEM were performed in SmartPLS v3.0 package (Ringle et al., 2015). As previously mentioned in the literature section, PLS-SEM is a suitable method in the case of smaller samples and according to the literature PLS-SEM gives much more accurate results, especially if data are not normally distributed. The sample of 50 consideration units (projects) collected in this study can be considered as a smaller sample for multivariate analyzes. The final model has seven manifest variables for engaging stakeholders, three variables for quality / scope, three for time execution and one for cost execution Hypothesis 1 and Hypothesis 3 were confirmed, and Hypothesis 2 was rejected, and.e the engagement of stakeholders have causal effect on the successful performance of time, quality and scope, and does not have a statistically significant effect on the project cost! 7. Defining success factors for the implementation stakeholder engagement and the development of a framework model for the engagement of key stakeholders in infrastructure projects As part of the data collection, eight interviews were conducted with various profiles of experienced experts in the field of project management, design, execution and other key functions in infrastructure construction projects. The analysis of these interviews, which cover a broader aspect of the engagement of stakeholders in infrastructure projects in Croatia, served the purpose of collecting and analysing data that are important for forming a framework for stakeholder engagement applicable in a real context. It is important to note that the project manager may be an employee of the client organization (contracting authority) or may be engaged through a public tender as an external service provider. They are primarily responsible to engage the project stakeholders. On the other hand, there are factors that neither the client (contracting authority) nor the project manager can influence, or they can only partially influence and these factors are related to the broader context of the project, such as legislation or project financing rules. The framework that is presented in this dissertation has a basic structure through three levels: • Level 3 - Level of the broader context of the project - success factors that affect changes that are not within the direct influence of the client and project manager • Level 2 - Level of the client's organization - factors of successful performance that require the implementation or changes of organizational processes • Level 1 - Level of operational project management - successful performance factors that require the implementation of activities / processes at the level of action of the project manager and project team Verification of this framework model was made through semi-structured interviews in which respondents with experience in implementing infrastructure projects evaluate the framework model according to six criteria with a score from 1 to 5, and on top of the ratings themselves were asked to leave comments. 8. Discussion and conclusion Each research, in addition to providing certain conclusions on previously set hypotheses, also opens some new theses and elements that should be researched, which would make an additional contribution in a particular area of research. Below are some possible future research on a related topic of this dissertation: • Examine the impact of engagement of stakeholders, but on a sample of all types of the construction projects or on some specific types to see if the causal relationships obtained in this research are valid in other contexts • Quantitatively examine whether certain contextual variables have an impact on the successful implementation of the engagement of stakeholders (for example, the experience of the client in the procurement of construction projects) • Examine (on a larger sample for both groups of projects) whether there are significant differences between the causal relationships of AIS and successful performance for social infrastructure projects (e.g hospitals, schools) versus AIS and civil infrastructure (e.g railways, agglomerations)