XRP is the native currency of the Ripple network. XRP are currently divisible to 6 decimal places, and the smallest unit is called a drop with 1 million drops equaling 1 XRP. There were 100 billion XRP created at Ripple's inception, with no more allowed to be created according to the protocol's rules. As such, the system was designed so XRP is an asset with decreasing available supply. Not dependent on any third party for redemption, XRP is the only currency in the Ripple network that does not entail counterparty risk, and it is the only native digital asset.
