There is no credible scientific information to date that supports the existence of werewolves. Many scholars who study the history of werewolves disagree among themselves about what exactly a werewolf is, making it harder still to prove or disprove their existence.
There are a number of case studies detailing the existence of werewolves with possible proof of encounter, but none to date have been verified or determined to be credible. Most people think of werewolves as mythical beings that can shapeshift into a wolf-like creature, generally when the moon is out. This is also how modern books, movies and television portray these creatures.