I will give a (biased) review on the main current ideas to explain the fundamental nature of Dark Energy using string theory. The possibility of a de Sitter vacuum in string theory, corresponding to a cosmological constant with w=-1, has proven difficult to achieve, leading to the conjecture that such vacua might lie in the String Theory Swampland. Other interesting string candidates include axion or runaway quintessence. I will in particular discuss the Thermal Dark Energy proposal. Here finite temperature effects in a light hidden sector hold a hidden scalar away from the minimum of its zero-temperature potential, leading to an effective cosmological constant, consistently with the Swampland Conjectures and with potentially observable consequences. [please email a.held@imperial.ac.uk for zoom link or password]