Today's business environment requires that companies, regardless of their size or structure, constantly consider and adopt new business approaches, methods, and management strategies. One of the strategies that allows for the optimisation of all the operational factors and is suitable for any business activity is outsourcing. The rationale behind it is that the company can focus on its core business and outsource all non-core activities to specialised companies. Businesses must comply with accounting and tax regulations and laws. Rather than being just a legal requirement, it is a clear need for any company striving to ensure more effective decision- making and successful business development. The doctoral thesis focuses on the sector of Small and Medium Enterprises (SMEs) in the Republic of Croatia, whose characteristics make it most suitable for externalisation. It should be noted that SMEs play a key role in any national economy since they are the main source of innovation and skills, and Croatian economy is no exception in this respect. In line with numerous definitions, outsourcing is understood as contracting out of non-core activities/services/processes. Although these might be ancillary activities in a particular company, they are still essential for production of goods or provision of services, but they are subcontracted to a company specializing in those activities. Furthermore, this relationship is usually based on a stable, long-term cooperation agreement with the service provider, who becomes a strategic partner. This whole process should be founded upon trust, open communication and cooperation between the receiver and provider of outsourced services, and all these factors are increasingly considered as the key issues in outsourcing. Literature review reveals that accounting services are outsourced to a great extent, which makes this topic particularly important and interesting. First, one needs to take into account the importance of the accounting function as such and how careful a company should be when choosing the outsourcing partner. Various statistics show how global market of outsourced services has been growing and is now of impressive size. Outsourcing of accounting services/activities is part of a broader concept, known worldwide as Finance and Accounting Outsourcing (FAO), which encompasses transfer of all or part of financial and accounting functions to an external (professional) accountant, with the aim of reducing costs, gaining access to highly professional skills and achieving competitive advantage. Foreign literature abounds with various relevant and influential theories of strategic management that might be suitable for the research of topics under consideration in the thesis. The following business theories were used as the theoretical framework: Transaction cost economics (TCE), Resource - Based Theory (RBT), Upper Echelons Theory, and Agency Theory. The main research topic in this doctoral thesis is the impact of accounting outsourcing on business performance of SMEs in the Republic of Croatia. The whole process preceding the implementation, i.e. the decision to outsource accounting services is crucial for understanding the big picture and delving into the main research topic. This is why different internal and external factors are included in the main research topic in order to determine their strength and impact on the decision whether to outsource accounting services, and ultimately their impact on SME performance. The main purpose of the doctoral thesis was to conduct primary research in the Republic of Croatia in order to investigate - in theory and empirically – the types and strength of impact, as well as interdependence of different factors that potentially influence decisions on accounting outsourcing and how that decision reflects on SME performance. Therefore, identifying the influential factors of accounting outsourcing and defining how such outsourcing affects the performance of SMEs in the Republic of Croatia were the main goals of the research presented in the doctoral thesis. The research was carried out in three phases. The first phase encompassed gathering and in-depth analysis of relevant secondary data on the research topic. On the basis of existing theories a conceptual research model was developed, which was tested and modified in further phases of research. The second phase included primary data collection by means of a research instrument in the form of a highly structured questionnaire. The survey was conducted on a sample obtained from the target population of SMEs operating in the Republic of Croatia. In the third phase, the data obtained in primary research were analysed and the research hypotheses were tested. The results of primary research were analysed using the Statistical Package for the Social Science (SPSS) ver. 21.0 for Windows. The process encompassed descriptive analysis, univariate, bivariate and multivariate statistical analysis, whereas structural equation modelling was carried out by means of the program AMOS for SPSS ver. 21.0. The scientific contribution of the doctoral thesis can be viewed from different aspects – it can be theoretical, applicative and methodological. The theoretical contribution of the doctoral thesis lies primarily in the comprehensive and systematic literature review accompanied by a summary of the key insights and conclusions, and applying the postulates of different strategic theories that have not been previously used by Croatian researchers who investigated similar topics. Having this in mind, the domestic literature on accounting is enriched with new insights and ideas, which can be further applied in the research of outsourcing of accounting services/activities. Furthermore, the topic was observed and examined in terms of different aspects, which provided an external and internal view of the outsourcing process. In terms of application, the contribution of the doctoral thesis lies in the identification of significant factors in the process of accounting outsourcing. All the factors are studied and evaluated, leading to concrete conclusions as to the impact of outsourcing on the company performance and its operations in general. This contributes to the practical aspect of the research, which provides useful information to all the companies that are considering, introducing or planning to apply the outsourcing concept in their operations. The scientific contribution can also be defined in methodological terms, namely, it can be characterized as both scientific and applicative. This refers to the development of completely new scales for two model variables (which were necessary, and to the adaptation of existing (foreign) measurement scales to the Croatian language and the business environment of the Republic of Croatia. Structural modelling in the context of this research topic is a new methodological approach in Croatia, not only in the research area of the doctoral thesis, but also generally in accounting. Structural modelling provided an insight into interrelationship of all the variables in the research model. Given the limitations, primarily the sample size and model complexity, the obtained results can be viewed as satisfactory. Moreover, these results can be an inspiration and a good basis for future research. The results of primary research indicate that the influential factors of accounting outsourcing are: Resource and competences deficit (within the company), Frequency of accounting activities, Technical competences (of accounting services bureaus), Reliability, security and trust (of the SME owner/manager) in an external accountant/in the professional Accountant, and the price (cost) of outsourcing accounting services. The examination of the overall research model (Structural Equation Modelling - SEM) has not revealed a direct impact of accounting outsourcing on business performance. However, some factors that have an indirect impact have been identified. Since their impact is reasonably steady, these factors are important for drawing conclusions and making recommendations in this particular research area, as well as for proposing future research directions. Outsourcing of accounting services has been shown as a potentially powerful tool/instrument/strategy for all SMEs that are aware of their own limitations in terms of resources and/or capabilities required for dealing with accounting tasks adequately. With this awareness comes the necessity to make up for their internal deficiencies – lack of knowledge, assets and employees. At the same time, cost reduction is never the only motive or goal of successful SMEs. When such companies outsource non-core functions such as accounting, owners/managers and their employees can focus on strategic activities that can bring added value, which in turn reinforces the human resources potential to contribute to their company's performance. According to the results of primary research, when the surveyed companies outsource their accounting functions, they want to achieve some higher goals, i.e. the reasons are not only cost reduction or because they have no choice. Such results confirm the essence of outsourcing – it is, or at least it should be, a method of improving strategic activities since it allows companies, its management and employees to focus on their core business. Outsourcing should be based on solid relations with service providers and a high level of mutual trust. When it works well, it enables (long-term) improvement of company performance, which is shown by financial indicators of profitability, but also experienced on a personal level.