Since the mid 1990s, Type Ia supernovae (SN Ia) have been successfully used to measure the expansion of the Universe. Careful observations of these spectacular stellar events, resulting from the thermonuclear explosion of white dwarf stars, have led to the groundbreaking discovery of the universe's accelerating expansion. Today, they remain essential in trying to characterize dark energy, a mysterious “vacuum” energy presumed to be causing the acceleration of the expansion. The talk will focus on the critical role of SN Ia as “calibrated standard candles" for measuring cosmic distances. I will describe current observational efforts and challenges as well as future large programs, which aim at gathering precise measurements of (ten of) thousands of SN Ia, from the ground as well as from space.
