Whereas in the first few years of the blockchain industry one may be forgiven for thinking that there would be only" one blockchain to rule them all", in recent times such a possibility has been receding further and further from reality. Within the public blockchain space, different projects have been staking out different regions of the tradeoff space between security, privacy, efficiency, flexibility, platform complexity, developer ease of use and even what could only be described as political values. In the private and consortium chain space, the notion that there exist different chains for different industriesand even different chains within the same industry-is even less controversial and arguably universally understood as obvious. In such a world, one natural question that emerges is: how do these chains interoperate? One of the advantages of using platforms where cryptographic authentication is naturally baked into every single operation is that we can actually provide much tighter and more secure coupling between platforms than is possible with previously existing systems. We can go far beyond the approach most common in centralized systems of simply having an API from one chain to the other, and in some cases even go so far as to have smart contract code on one chain verify the consensus finality of events on other chains directly, requiring no trust in intermediaries at all.

Interoperable chains open up a world where moving assets from one platform to another, or paymentversus-payment and payment-versus-delivery schemes, or accessing information from one chain inside another (eg." identity chains" and payment systems may be a plausible link) becomes easy and even implementable by third parties without any additional effort required from the operators of the base blockchain protocols. So far the notion of chain interoperability has seen much theory and little practice, primarily because a live example of successful chain interoperability requires not one, but two, already existing, stable and sufficiently powerful blockchains to build off of, but this is slowly starting to change.