The nature of the source currently dominating the energy density of the universe and leading to it’s observed acceleration is still a mystery. A cosmological constant remains the best fit in many ways but recent results coming from the DESI collaboration suggests it could be dynamical in nature. Both possibilities are problematic! In this talk we will review the possibilities, emphasising some of the theoretical issues faced by both a cosmological constant and dynamical dark energy. The bottom line - I don’t know what’s going on but it’s fun thinking about these big questions !