Abstract: With the increasing interest in the potential use of blockchain systems for virtual assets, there is a need for these assets to have mobility across blockchain systems. An interoperability architecture for blockchain systems is needed in order to permit the secure flow of virtual assets between blockchain systems, satisfying the properties of transfer atomicity, consistency and durability. The architecture must recognize that there are different blockchain systems, and that the interior constructs in these blockchains maybe incompatible with one another. Gateway nodes perform the transfer of virtual assets between blockchain systems while masking the complexity of the interior constructs of the blockchain that they represent.