  The idea of a negative-pressure dark energy component in the Universe which
causes an accelerated expansion in the late Universe has deep implications in
models of field theory and general relativity. In this article, we survey the
evidence for dark energy from cosmological observations which started from the
compilation of distance-luminosity plots of Type Ia supernovae. This turned out
to be consistent with the dark energy inferred from the CMB observations and
large scale surveys and gave rise to the concordance $\Lambda$CDM model of
cosmology. In this article, we discuss the observational evidence for dark
energy from Type Ia supernovae, CMB, galaxy surveys, observations of the
Sunyaev-Zeldovich effect from clusters, and lensing by clusters. We also
discuss the observational discrepancy in the values of $H_0$ and $\sigma_8$
between CMB and large scale structures and discuss if varying dark energy
models are able to resolve these tensions between different observations.
