The universe is in a period of accelerated expansion; and the observational evidence such as supernova of Ia type, Cosmic Microwave Background radiation (CMB) and Baryon Acoustic Oscillations (BAO) confirm this accelerating expansion [1-3]. Despite the great number of observational evidence, the responsible mechanism for this accelerating expansion is still unknown, and thus several models have been proposed for this phenomenon[4-18]. The simplest proposed model in the general relativity is a cosmic model with a dominant component that is considered as a fluid with negative pressure and constant density[8] (means Dark Energy component) . In this book, we consider effects of Dark Energy content on the universe. Accordingly, structure of discussions in the present book was on four chapters as follows: chapter 1 : Dark Energy, Motivation and Candidates, chapter 2 : The Equivalence Principle Applicability Boundaries,Measurability, Gravity and Dark Energy Problem, chapter 3 : The Behaviors of a Candidate for Dark Energy from ur-Higgs Boson , and chapter 4 : Non-equilibrium Evolution of Quantum Fields During Inflation and Late Accelerating Expansion . However, I hope this collection of context will be useful for readers to understand more accurately the dark energy idea.