Αντικείμενο της παρούσας διατριβής υπήρξε αφενός η μελέτη και η αξιολόγηση των υπαρχόντων τεχνικών και αφετέρου ο σχεδιασμός, η υλοποίηση και η αποτίμηση νέων τεχνικών και μηχανικών για τη βελτιστοποίηση της απόδοσης του συστήματος με τη βέλτιστη αξιοποίηση των διαθέσιμων πόρων. / The objective of this dissertation was on the one hand the study and analysis of existing techniques and algorithms for large-scale DVEs and on the other hand the design, implementation and assessment of new techniques, methods and algorithms that can ensure the quality of the provided services and the efficient operation of the system. The algorithms and techniques developed were analysed and evaluated through extensive experiments both for identifying possible weaknesses and for highlighting the applications that can achieve optimum results. More specifically, two approaches have been designed and developed. The first approach is related to the design and development of a partitioning algorithm, that, in contrary to existing approaches, exploits the special characteristic of the virtual world and the impact those characteristics have on users’ behavior in order to predict the needs of the environment, in terms of resources, before they are required. The second approach is related to the design and development of a dynamic management approach that exploits the dynamic nature of DVEs in order to perform load balancing and to ensure performance optimization. During the elaboration of this dissertation, we found out that one of the basic problems when designing and implementing algorithms, methods and techniques for large-scale DVEs is the way that their efficiency could be examined. In most of the cases, the evaluation is based on theoretical models, which often fail to meet the circumstances and situations met in real DVEs. In particular, for supporting largescale DVEs, extended infrastructure is needed in terms of both hardware and software. Due to the fact that both researchers and application designers do not always have access to such extended infrastructure, the assessment and evaluation of developed techniques are extremely difficult. In most of the cases, both application designers and researchers adopt specialized methods for evaluating different techniques, while in other cases simulation tools have been developed from scratch. However, given the fact that the design and implementation is application or technique-specific, the reusability of these tools for different architectures and algorithms is not always successful. To this direction and for overcoming this important limitation, a simulation modeling framework for assessing DVEs performance was designed and implemented. The framework takes into account a number of both generic and special-cause parameters, which can be set on demand by the DVE designers and stake-holders and it is based on transforming system requirements to the concepts of operational management.