The purpose of this article is to improve the theoretical and methodological foundations for studying the essence and peculiarities of development of the institutional environment of the digital economy sector, to allocate the components of its architectonics as the basis for forming a platform for the conceptual development of the national economy based on digitalisation. Methodology. The methodological basis of the study is formed by modern economic and sociological institutional theories, the object of analysis of which is the institutional dynamics of the environment: institutional theory, new institutional theory, substantivist theory, the concept of institutional density, the concept of institutional matrices, the theory of societal psyche. The paper uses the historical-logical and dialectical methods to study the contradictions of the processes of formation and development of the institutional environment, as well as the methods of system analysis to study the components of the architectonics of the institutional environment of the digital economy. Results. From the standpoint of institutional theory, it is formulated and substantiated that the institutional environment of the digital economy sector is a synthesis of a set of formal/іnformal basic/complementary institutions of the traditional and digital economies of different levels and institutions that are in certain interconnections and relationships with each other, forming a hierarchical integrity. Institutions determine the creation and operation of relevant institutions, which, in turn, ensure the implementation and enforcement of established rules and regulations. At the same time, the resilience and flexibility of the environment is based on the natural accumulation or forced implementation of basic institutions capable of ensuring the emergence of new digital economy institutions or significant modernisation of existing ones, which protects and promotes the development of the digital economy. The task of managing the institutional environment is to balance the ratio of institutions. The architectonics of the institutional environment of the digital economy sector is a system that combines a functional set of institutions of the traditional economy (management, labour, property, market, non-market), specific institutions of the digital economy (information, participation, digital space), global institutions, and regional institutions. Institutions as systemic elements, through implementation/legitimation mechanisms, form a set of institutions of the digital economy that mediate the interaction of economic actors, provide contracting, and mechanisms of institutional change. The most important institutions include innovation labs, research centres, technology companies, start-ups, cryptocurrency exchanges, digital agencies, consultancies, educational institutions, learning platforms, government agencies, legislative bodies, banks, digital banks, financial institutions, digital platforms, and digital networks. Interaction and mutual influence of institutions and institutions of the digital economy form the guidelines for selecting effective elements of the institutional structure from alternative institutional forms. The digitalisation of Ukraine, which is focused on the norms of international, European and regional cooperation, will facilitate Ukraine's integration into the European and global market of e-commerce, goods and services based on information and communication technologies. A new global economic architecture is being designed, into which new economic agents are integrating. At the same time, regionalisation processes are taking place, new regional clusters are emerging, and the country is being integrated into the European cluster. Practical implications. The elements of the architectonics of the institutional environment of the digital economy sector are identified and summarised by criteria, which makes it possible to identify the most problematic areas of institutional transformations and to formulate and select instrumental solutions to overcome them. The development of the relevant elements of the institutional environment of the digital economy sector contributes to a rapid and profound digital transition, when the results of digital transformation will become the basis of Ukrainian society and a key factor on the path to Ukraine's prosperity and welfare. Value/оriginality. It is established that the use of institutional analysis tools will allow determining the optimal directions of institutional building/transformation of digital economy institutions and minimising the social costs of Ukraine's evolutionary development. A two-level approach to designing the institutional environment of the digital economy sector in the national space is proposed: at the institutional level – as designing the socio-political and economic conditions for the development of digital economy institutions based on the development of digital products and technologies; at the individual level – as designing the functional place of a digital product in the human life space.