Observations suggest that the initial conditions of the history of the Universe were set by a period of superluminal expansion of space, called Cosmic Inflation. Furthermore, they also confirm that the Universe has recently entered a new inflationary era. General relativity suggests that this behaviour of space requires the dominant presence of an exotic substance, called Dark Energy. Therefore, Dark Energy holds the key to the origin and the fate of the Universe. In this talk, I will review how inflation is modeled in particle theory and how the two eras of primordial and late inflation can be linked in the context of a single theoretical framework. This quintessential inflation can produce characteristic observational signatures, such as a spike in primordial gravitational waves, which will be probed in the near future.