Evidence from Type Ia Supernovae for an Accelerating Universe and Dark Energy

I review the use of Type Ia supernovae (SNe Ia) for cosmological distance determinations. Low-redshift SNe Ia (z 0. Most recently, analyses of SNe Ia at z = 1.0 - 1.7 provide further support for current acceleration, and give tentative evidence for an early epoch of deceleration. Current projects include the search for additional SNe Ia at z > 1 to confirm the early deceleration, and the measurement of a few hundred SNeIa at z = 0.2 - 0.8 to determine the equation of state of the dark energy, w = P/(ρc^2).