A Bill Switch, also known as a Bill Change, is a generic term for all techniques wherein a bill (as in currency) is apparently changed into (while actually being exchanged for) another bill, frequently during the process of folding it, then unfolding it at the fingertips. Most contemporary techniques are an outgrowth of “The $100 Bill Switch,” invented by circus performer Vladimir Vladimirov, but popularized by Mike Kozlowski, who released his handling as a manuscript in 1977 (Hundred Dollar Bill Switch). It has proven to be one of the strongest and most popular effects in all of close-up magic.
The original effect: A $1 bill is folded into sixteenths and then unfolded in an extremely fair manner, showing it to have changed into a $100 bill.
The technique used lends itself to many other routines, and has inspired much creative thinking since its advent.
In some more recent variations, the bill is folded less (i.e., into eighths, or quarters, or even just in half, as opposed to sixteenths), allowing for a more visual transformation. These include Richard Sanders' Visi-Bill, Sean Fields' Infinity Switch, and Juan Pablo's Juan Hundred Dollar Bill Switch.
See also Easy Money.