A primer on Blockchain, Semantic Web and Ricardian Contracts. Semantic Blockchain is a proposal where the Semantic Web meets the Blockchain. Combining these two technologies could provide the Semantic web with a transparent proof of work and trust mechanism while conversely disambiguating data stored on the blockchain, solving one of the key challenges with Riccardian/Smart contracts. This presentation will explore how these two technologies might be combine using the example of a smart contract. However the potential application is much bigger and could provide a key back bone underlying the Internet of Things.