Internet growth in the nineties supported government ambition to provide better services to citizens through the development of Information and Communication Technologies based solutions. Thanks to the Lisbon conference, which in 2000 covered and investigated this topic, e-government has been recognized as one of the major priorities in Public Administration innovation process. As a matter of fact in the last 10 years the number of services provided to citizens through Information and Communication Technologies has increased rapidly. Nevertheless the increasing rate, the access and usage of digital services do not follow the same trend. Nowadays Public Administrations deliver many electronic services which are seldom used by citizens. Different reasons contribute to the highlighted situation. The main assumption of the thesis is that quality of e-government digital services strongly affects real access to services by citizens. According to the complexity of quality in e-government, one of the main challenges was to define a suitable quality model. To reach such aim, domain-dependent characteristics on the services delivery have been investigated. The defined model refers to citizen, technology and service related quality characteristics. Correspondingly a suitable way to represent, assess, and continuously improve services quality according to such domain requirements has been introduced. Concerning the service related quality aspects a methodology and a tool permitting to formally and automatically assess the quality of a designed service with respect to the quality model has been defined. Starting from an user friendly notation, both for service and quality requirements, the proposed methodology has been implemented as an user friendly tool supported by a mapping from user friendly notations to formal language. The tool allows to verify formally via model checking, if the given service satisfies one by one the quality requirements addressed by the quality model. Additionally in some case an unique view on e-government service quality is quite useful. A mathematical model provides a single value for quality starting from the assessment of all the requirements defined in the quality model. It relies on the following activities: homogeneity, interaction and grouping. A set of experiments has been performed in order to validate the goodness of the work. Services already implemented in a local Public Administration has been considered. Literature review and domain experts knowledge were the main drivers of this work. It proofs the goodness of the quality model, the application of formal techniques in the complex field of study such as e-government and the quality aggregation via the mathematical model. This thesis introduces advance research in e-government by providing the contributions that quality oriented service delivery in Public Administration promotes services used by the citizens. Further applications of the proposed approaches could be investigated in the areas of practical benchmarking and Service Level Agreement specification.