  I present a brief review on the determination of the primordial helium
abundance by unit mass, Yp. I discuss the importance of the primordial helium
abundance in: (a) cosmology, (b) testing the standard big bang nucleosynthesis,
(c) studying the physical conditions in H II regions, (d) providing the initial
conditions for stellar evolution models, and (e) testing the galactic chemical
evolution models.
