The invention of the printing press was crucial to the spread of the Protestant Reformation. In addition to spreading Martin Luther's ideas during the early years of the Reformation, the printing press helped spread John Calvin's version of Protestantism throughout Europe. Before the invention of the printing press, scribes had to copy books by hand. This was a laborious process, so books were incredibly expensive. For example, a single scribe would have to work as long as a year to produce one copy of the Bible.
Johannes Gutenberg's printing press made the process much faster. Thus, printers could produce more books at less cost. This allowed Calvin's writings--most notably his Institutes of the Christian Religion, which outlined the main tenets of what would soon be known as Calvinism--to spread across Europe at a far more rapid pace than would have been possible several centuries earlier.