  The "Spinors" software is a "Mathematica" package which implements
2-component spinor calculus as devised by Penrose for General Relativity in
dimension 3+1. The "Spinors" software is part of the "xAct" system, which is a
collection of "Mathematica" packages to do tensor analysis by computer. In this
paper we give a thorough description of "Spinors" and present practical
examples of use.
