I will introduce and discuss observations which in modern cosmology let to the conclusion
that the expansion of the Universe is accelerating. I will introduce how theoreticians aim to
model the accelerated expansion and how observables are constructed to shed further light on
this mysterious dark energy. I will elaborate on recent findings about the nature of dark energy and 

will highlight how future observational campaigns, like the Euclid satellite, aim to shed light on 

the properties of dark energy.