We discuss the methods of determining the number of neutrino species N_ν, one of the most important numbers in particle physics and playing an important role in the Big Bang nucleosynthesis. As useful measures for the N_ν, we consider the reactions: [numerical formula]+anything, [numerical formula]+anything, [numerical formula]+anything, [numerical formula]+anything, and [numerical formula]+anything, most of which are discussed for the first time in this article. Particular emphasis is placed upon the transverse momentum spectra in the reaction: [numerical formula]+jet+anything, accomp-anying a hadronic jet with large transverse momentum
