Blockchain is a distributed ledger and its data immutability property solves various data security issues. Every participant has a copy of data and validates it, hence removing a third party to verify the correctness of data. Smart contract is a programmatically written set of rules that reside on the blockchain which allows the execution of business logic when certain conditions are met and brings in automation with trust and safety for the data. This paper focuses on understanding blockchain, its features, challenges, types, and how its integration can be an advantage in IoT. The challenges faced in the integration of Blockchain and IoT is summarized and a study on the existing IoT-blockchain applications for smart city is done.

Keywords : IoT; Blockchain; Distributed Ledger; Smart Contract; Smart City.