The proper usage of Type Ia supernovae (SNe Ia) as distance indicators has
revolutionized cosmology, and added a new dominant component to the energy
density of the Universe, dark energy. Following the discovery and confirmation
era, the currently ongoing SNe Ia surveys aim to determine the properties of
the dark energy. ESSENCE is a five year ground-based supernova survey aimed at
finding and characterizing 200 SNe Ia in the redshift domain z=[0.2-0.8]. The
goal of the project is to put constraints on the equation of state parameter,
w, of the dark energy with an accuracy of <10%. This paper presents these
ongoing efforts in the context of the current developments in observational
cosmology.Comment: Submitted to EPS1