The current energy crisis has raised important policy questions on how to strengthen short-term energy security while remaining firmly committed to the green transition, a challenge amplified by the recent consensus at COP28 to transition away from fossil fuels. This paper examines the historical determinants of the security of energy supply and analyzes the green transition implications for energy security. Looking back, find that the diversification of energy trade partners, or the lack thereof, was the main factor that underpinned energy security dynamics within and across countries over the last two decades. Looking ahead, the green transition is expected to have a net positive effect on energy security provided investments are aligned to address new challenges posed by the increased reliance on renewables.