In his thesis the Author presents research which he conducted as part of his final postgraduate doctoral studies at the Mechanical Engineering Faculty in Slavonski Brod. This research related to the search for opportunities to improve production process results through the application of Lean principles on small and medium-sized enterprises. The introductory part of this thesis defines the motivation for choosing this research topic, current knowledge about the research problem, the goal and hypothesis of the thesis itself, the research method and work structure applied and the expected scientific contribution. Following the introductory chapter, the basic characteristics of Lean methodology are outlined through a description of the term of ‘Lean’, the history and the modern principles of Lean and an appraisal of the contribution of ‘gurus’ within the Lean concept. The term and principles of improving production processes are described in a separate chapter as this is an extremely important activity within the Lean concept. A specific form of a suggestion has been specifically indicated in the analysis of the needs for improvements, procedures and improvement factors, as this activity is very important for initiating and implementing improvements. Whilst exploring this issue the thesis cites many examples that relate to the different experiences of Japanese and American companies, as well as those of other countries. Chapters 4 and 5 relate to losses in the production processes and those Lean techniques that are used most often in implementation procedures for specific activities. By defining the term of ‘losses’ in production processes and providing a brief description of each loss the Author has tried to show their importance, and also emphasise the even greater importance of ‘fighting’ these losses. The most common techniques (tools and methods) used in the Lean concept are briefly outlined. As is the case for losses, they indicate the need for further research and analysis. In Chapter 6 the Author presents the results of research conducted on Croatian small and mediumsized enterprises and in the academic community within the Republic of Croatia and abroad. By analysing a large amount of information and data the author presents research relating to the selection of priority losses, research related to the application of Lean techniques and research related to the identification of dominant barriers presenting obstacles to the more systematic application of Lean concepts in small and medium-sized enterprises. The results of this research were used to design a specific Lean concept model (MSP–LK) for small and medium-sized enterprises. This model was conceived through 8 modules that require application in implementation procedures. In Chapter 7 the author describes these modules and their specific features and presents some of the real examples of their application in the real sector. The Conclusion states that the conducted research and verification of the research confirmed the possibility to adapt and apply Lean methodology to small and medium-sized enterprises within the Republic of Croatia. The proposed model is based on the modern principles of the Lean concept, the experiences of larger companies, the characteristics of small and medium-sized enterprises and the experiences gained by the author during the course of this research and the study of an extensive range of scientific literature. The author is convinced of the successful potential of the proposed model for small and mediumsized enterprises involved in production in addition to those companies involved in other activities, taking into account the necessity to adjust to the specifics of these businesses.