The present understanding of inflationary cosmology suggests
that our universe is one among an infinite number of ``pockets''
in an eternally inflating multiverse.
A realistic model of the multiverse has a physical volume that
diverges with time. A method to regularize the infinities is
required to extract physical predictions.I will review the mechanism of eternal inflation and some of the proposals to regularize the volume of the multiverse.
The focus will then be on the ``scale-factor time cutoff
measure'' and on its properties.