This paper reviews various approaches to explain the observed acceleration of the universe, focusing on the nature of dark energy. It discusses observational evidence for the current accelerated expansion, including supernova data, the age of the universe, and cosmic microwave background (CMB) and large-scale structure (LSS) observations. The paper explores different models of dark energy, such as the cosmological constant, quintessence, K-essence, tachyon, phantom, and dilatonic models. It emphasizes the importance of cosmological scaling solutions in studying the dynamics of scalar fields, including coupled dark energy. The evolution of cosmological perturbations is studied to confront observations of the CMB and LSS, and methods for reconstructing the equation of state of dark energy using supernova data are discussed. The paper also delves into tracking solutions in cosmology, particle physics, and braneworld models, the nature of future singularities, the effect of higher-order curvature terms, and modified gravity theories that can explain late-time acceleration without invoking dark energy.This paper reviews various approaches to explain the observed acceleration of the universe, focusing on the nature of dark energy. It discusses observational evidence for the current accelerated expansion, including supernova data, the age of the universe, and cosmic microwave background (CMB) and large-scale structure (LSS) observations. The paper explores different models of dark energy, such as the cosmological constant, quintessence, K-essence, tachyon, phantom, and dilatonic models. It emphasizes the importance of cosmological scaling solutions in studying the dynamics of scalar fields, including coupled dark energy. The evolution of cosmological perturbations is studied to confront observations of the CMB and LSS, and methods for reconstructing the equation of state of dark energy using supernova data are discussed. The paper also delves into tracking solutions in cosmology, particle physics, and braneworld models, the nature of future singularities, the effect of higher-order curvature terms, and modified gravity theories that can explain late-time acceleration without invoking dark energy.