Accelerating Universe: Observational Status and Theoretical Implications

This is a pedagogical review of the recent observational data obtained from type Ia supernova (SnIa) surveys that support the accelerating expansion of the universe. The methods for the analysis of the data are reviewed and some of the theoretical implications obtained from their analysis are discussed. In particular, the existence of dark energy with negative pressure required by the data is demonstrated and the simplest type of dark energy (the cosmological constant) is shown to fit well the SnIa data. Dynamical forms of evolving dark energy are also shown at their best fit form to the data and their common features are discussed.