Neutrinos play prominent roles in both particle physics and cosmology. In
this talk, I will cover two broad topics. The first will be possible origins
for neutrino masses and mixings and the implications of this physics for
cosmology. Some non-cosmological digressions on the flavour problem in general
will be made. The second topic will be Big Bang Nucleosynthesis (BBN) and
bounds on active-sterile neutrino mixing.Comment: 19 pages, 6 figures. AIP proceedings style. Invited talk at 3rd
Tropical Workshop on Particle Physics and Cosmology, San Juan, Puerto Rico,
Aug 19-24 2002. To appear in the proceeding
