  We discuss constraints on the effective number of neutrino species Nnu from
recent cosmological observations such as CMB, LSS, BBN, including our own
analysis which uses the WMAP and the Luminous Red Galaxy power spectrum data.
We also discuss their implications on some non-standard cosmological scenarios
such as the low (MeV-scale) reheating temperature scenario and the scenario
with decaying particles between BBN and structure formation.
