This doctoral thesis focuses on the impact of communication quality and shared mental models of information and communication technology (ICT) on virtual team performance. The Task- Technology Fit (TTF) model was chosen as the theoretical basis and framework for the empirical research in the dissertation, involving members of virtual teams employed in information and communication technology (ICT) companies in the Republic of Croatia. The main problem of this dissertation is to investigate the influence of communication quality and shared mental models of information and communication technology on task-technology fit on the one hand, and on the performance of members of virtual teams using communication platforms for task completion, on the other hand. In the introductory chapter of the doctoral thesis, a concise overview of the field of research on this problem is given and the shortcomings of existing studies on the success of virtual teams are pointed out. Research questions, objectives, and hypotheses are defined, and the expected scientific and societal contributions are highlighted. To achieve these goals, in the doctoral thesis, following the research steps for conducting design science, two artifacts are developed: 1) an extended conceptual model of Task-Technology Fit, and 2) a measurement instrument. The second chapter of the doctoral thesis elaborates theoretical concepts that are crucial to the research problem. First, virtual teams and the characteristics of teamwork in a virtual environment are explained. The theoretical model Task-Technology Fit (TTF) is described in detail with its key elements based on the existing literature. To answer the first research question, two literature reviews were conducted to identify a) key task characteristics and b) technology characteristics related to communication platforms that are associated with or influence virtual team performance. In addition, two variables were identified that are potentially important in explaining virtual team performance but have been little studied in the existing literature. The first variable is communication quality with four sub-dimensions - openness of communication, knowledge sharing, elaboration of information, and general information sharing. The second variable relates to shared mental models of information and communication technology, the importance of which is highlighted in research on virtual team performance. Virtual team performance is also discussed in this chapter. The chapter summary provides important guidelines derived from the literature review and implications for the empirical research conducted in this dissertation, particularly for the development of an extended Task-Technology Fit (TTF) model. III In the third chapter of the doctoral thesis, conceptual definitions of basic constructs of the extended Task-technology-fit model are given: a) technology characteristics, b) task characteristics, c) task-technology-fit, d) perceived performance, e) communication quality, and f) shared mental models of ICT. In addition, the chapter describes the development of three research hypotheses to be tested to determine the relationships among the variables in the extended TTF model. The fourth chapter deals with the methodological foundations of the doctoral thesis. The research in the doctoral thesis follows the six research steps for conducting design science: (1) problem identification and motivation; (2) definition of solution goals; (3) design and development; (4) demonstration; (5) evaluation; and (6) communication. These steps are described in detail, along with the activities that contribute to the development of two artifacts: (1) a measurement instrument and (2) an extended conceptual model of Task-Technology Fit. In addition, this chapter describes the target group of study participants and the method used to select a convenient sample of participants for the pilot study and the main study, which included employees in ICT companies in the Republic of Croatia. The fifth chapter of the doctoral dissertation, the research constructs, followed by a detailed description of the process of developing a measurement instrument through three basic steps: creating questionnaire items, developing measurement scales (constructs), and testing the questionnaire. These steps were complemented by mixed methods for developing and validating the measurement scales (constructs). To preliminarily establish the convergent and divergent validity of the constructs, a content validity assessment was conducted with the participation of nine experts and the closed card sorting method was used in two iterations. The application of these methods resulted in a reduction of the initial number of questionnaire items from 62 to 48. This chapter also presents the results related to the questionnaire testing, specifically in terms of its reliability and validity. For this purpose, a pilot study was conducted on a convenient sample of ICT employees, involving 143 respondents. Following the analyses, a reliable and valid measurement instrument with 45 indicators (items) was developed for data collection in the main study and hypothesis testing. In this phase, a reliable and valid measuring instrument was developed for data collection in the main study and the length of the questionnaire was optimised for the online testing. The sixth chapter of the doctoral dissertation presents the results of the main research, with the participation of 358 respondents. The research was conducted on a convenience sample of employees in ICT organizations who perform tasks in virtual teams. This chapter is related to IV the fifth step of the research process in the science of design - evaluation. As part of the evaluation, the extended conceptual model of task-technology fit was validated using data collected from 358 properly completed surveys (N=358) in the main study. Partial Least Squares Structural Equation Modeling (PLS-SEM) was used for structural equation modeling, and hypothesis testing was conducted using SmartPLS 4 statistical software. Because communication quality is defined and measured as a multidimensional construct in the dissertation, a disjunctive two-level approach was used to evaluate the first and second level reflective measurement models. Prior to evaluating the structural model, a fit test of the data was conducted using the statistical program IBM SPSS AMOS v.29. After all evaluation criteria relevant to the reflective measurement model were met (checking reliability of indicators, internal consistency, convergent validity, and discriminant validity of constructs), the structural model was also evaluated. This involved checking the collinearity, predictive accuracy, and predictive power of the model. Another important step related to the evaluation of the structural model is the testing of the significance of the correlations in the structural model, which allowed for the testing of the hypotheses made in the doctoral thesis, as well as other correlations between the research variables. In addition, a correlation analysis and an importance- performance map analysis of the structural model were conducted. In the seventh chapter of the doctoral thesis, the research findings are presented in the context of research hypotheses, objectives, and questions based on theoretical literature reviews and empirical research findings. In addition, the significance of the research findings is explained in relation to similar important scientific research related to the dissertation topic. The eighth chapter of the dissertation describes the scientific and societal contribution resulting from the different steps of the dissertation and proposes guidelines for future research related to the performance of virtual teams. The ninth chapter presents the limitations of the research conducted and other aspects of the dissertation