Today's dynamic environment requires companies to constantly adapt, which is mainly reflected in the application of new technologies, improvement of business processes and the acceptance and implementation of functions suitable for doing business in digital conditions. Given the growing amount of internal and external data that companies have and the benefits and challenges that this data provides to decision makers, there is a need for functions that, through their activities, can guide management to make effective business decisions. One of those functions is controlling, which provides adequate information to decision-makers, and which in large number of data selects and analyses the key ones, interprets them, and proposes solutions. According to its role, controlling should be one of the key information and advisory functions within today’s companies. Therefore, the purpose of this doctoral dissertation was to define and confirm the influential characteristics that in digital conditions determine the efficiency of the controllers' work and their impact on decision making, but also to prove the importance of controlling as a support to management. Hence, this dissertation aimed to explore and expand existing theoretical knowledge of controlling and to develop and validate a conceptual model for measuring the relationship of controllers, managers, companies, and environmental characteristics with the quality of controller’s outputs and its impact on decision-making. For empirical research and testing of the set conceptual model, i.e. hypotheses, in cooperation with four controllers, a survey questionnaire was developed whose validity and reliability were confirmed through a pilot testing on a sample of 21 controllers. The final sample of the research were 148 controllers and 64 managers from large, medium, and few small companies in the Republic of Croatia. The research involved testing the conceptual model through two samples. The first sample involved testing the model solely on controller responses, and the second on paired manager and controller responses. The multivariate statistical method of partial least squares structural equations modeling (PLS-SEM) was used to test the validity and reliability of the measurement model, and to confirm the set hypotheses and the exploratory and predictive power of the structural model. The results of the research confirmed the relationship between the set characteristics of the controllers, the company, and the environment with the quality of the controllers’ outputs, and the relationship between the quality of their outputs and the controllers' influence on decision- IV making. The research only did not confirm the relationship of managerial characteristics with the quality of the controller outputs, but it confirmed that managerial characteristics are significantly related to the controllers’ influence on decision-making. This was confirmed by examining the model from the perception of controllers, but also by involving managers through the evaluation of controllers’ characteristics, the quality of their outputs, and their impact on decision-making. In the second model, which includes perceptions of managers', only the relationship between the characteristics of the environment and the controllers’ influence on decision-making was not confirmed. In both models, proactivity proved to be the most important characteristic of the controllers, and in the case of managers, leadership and initiator. Strategic orientation was confirmed as the most important characteristic of companies, while the intensity of competitiveness was proven as the most valuable environmental characteristic. From the perception of controllers', it was also confirmed that the length of the controller's work experience in the field of controlling contributes to the quality of the controller's outputs and decision-making role. The importance of other set control variables has not been proven, except the way controlling is organized (centralized/decentralized/combined). Hence, it has been proven as an important control variable of the controllers’ influence on business decision-making only in the first model. Although the application of business intelligence has not been proven as a significant control variable of the quality of the controller's outputs, appropriate to the opinions obtained from the controllers on its usefulness and the need for wider application, it can be emphasized is that these tools will be an integral part of controlling in the future. Accordingly, the doctoral thesis is the basis for further research and improvement of given methodological and applied contributions, which are primarily reflected in the developed and confirmed conceptual model, the possibility of testing it in other countries, and its applications within companies for assessing internal effectiveness of controlling, but also the development of study programs for controlling. In addition, based on the acquired knowledge of empirical research and theoretical background, the thesis provides a proposal for the future development of controlling based on digitalization.