Dark Energy: Evidence and Future Prospects

I will review the ever-stronger observational evidence for the late-time acceleration of the expansion of the universe obtained from observations of the cosmic microwave background by the Planck satellite and the increasingly wide galaxy surveys. The data are grossly compatible with a cosmological constant, but increasingly there are hints that there are some anomalies. I will explain what is necessary to account for such anomalies and address how one might be able to explain them within the context of modifications of gravity.