The legality of Bitcoin depends on who you are, where you are in the world, and what youre doing with it.
Every single fiat currency in the world is created, released and controlled by a single entity in most cases a central bank. Bitcoin offers an efficient means of transferring money over the internet and is controlled by a decentralized network with a transparent set of rules, thus presenting an alternative to central bank controlled fiat money. As its becoming more and more mainstream, law enforcement agencies, tax authorities and legal regulators all over the world are trying to wrap their heads around the concept of cryptocurrency and where exactly does it fit in existing regulations and legal frameworks.