Energy transition emphasizes the role of local authorities towards a sustainable future: energy productions are increasingly more decentralized by valuing renewable energies often rooted in territories. Management and operation of local energy systems are becoming more complex due to this paradigm shift (grid and supply/demand balancing), especially because production and consumption are not synchronized and not spatially related (temporal and spatial discontinuity). Territorial energy systems approach, consisting in analyzing all energy aspects of a territory in an integrated and simultaneous way (needs, resources, conversion and storage technologies), provides a relevant answer to this issue. It allows to systematically consider a large number of solutions, different by nature, in term of energy vectors and technologies, and to compare them in term of global performances at a territory scale. Nevertheless, it requires a very large amount of data to be structures and secured, as well as powerful calculating algorithms, combining energy and information technology (IT) aspects: smart cities and smart grids. Moreover, a territorial energy approach helps to provide actual answers to local entities, mainly through informatics tools, in term of energy monitoring and planning. Some of these tools will be highlighted through concrete examples.