Smart city seeks to solve public issues through solutions based on information and communication technologies with the joint support of several stakeholders and local authorities. Cities generate an increasing amount of data that becomes a valuable resource if it is managed by using big data technologies. The main objective of the doctoral dissertation is to describe and examine the factors of adoption of big data technologies in cities of the European Union. The proposed research model is based on the literature review and the Technology - Organization - Environment framework. The survey is carried out in order to collect data. The target population of this research are cities of the European Union - EU28 countries with more than 40 thousand inhabitants. The evaluation of the research model was performed using the PLS-SEM method and related methods.In this research, Technological Readiness, Absorption Capacity, City Management Support, Existence of Smart City Strategy and Stakeholder Support were identified as factors that directly influence the Adoption of big data technologies in cities. Also, it has been shown that the Adoption of big data technologies directly influences the Use of data in decision making by city management. Furthermore, the moderating effect of City size on the connections between certain factors and the Adoption of big data technologies in cities is not significant. Additionally, the results of the empirical research are combined with the practical recommendations for smart cities development and key factors for the adoption of big data technologies in the European Union and Croatia.