General Relativity and the Cosmological Principle are the fundamental pillars of Cosmology. After introducing them and their underlying properties I will discuss the successes and challenges of the Standard Model of Big Bang Cosmology. I will then discuss how we can test General Relativity using different cosmological observations, from its geometrical properties down to testing the involved propagating degrees of freedom.
This analysis will also help us to classify the attempts of going beyond General Relativity together with their explicit implications.
