Buildings have both high as well as flexible energy demands and play an important role in the energy internet solution. The buildings' energy flexibility (BEF) is a widely recognized concept; however

how to unlock its potential is a relatively new research topic. In this paper

the authors provide an overview of the latest research related to BEF. An introduction to BEF is provided

methods developed for identifying and characterizing BEF are presented

and several key influencing factors are identified. The overview also covers various aggregation methods to scale up BEF impacts and service-oriented solutions for enabling BEF applications in different energy sectors. This work lays the groundwork for designing and developing seamless integration strategies for BEF use in both present and future energy systems.