CryptoKitties are digital, collectible cats built on the Ethereum blockchain. They can be bought and sold using Ethereum, and bred to create new cats with several traits and varying characteristics. Two CryptoKitties can breed to produce a new cat that is the genetic combination of its parents. The possibilities for new and rare genetic makeups of a CryptoKitty are endless. In each breeding pair, one cat acts as the sire and will have a recovery period before it can breed again.