This document discusses using blockchain technology to build more secure Internet of Things (IoT) solutions. It begins by outlining some of the major security challenges facing IoT, including high-profile hacks that have impacted systems like HVAC and medical devices. It then provides an overview of blockchain technology, explaining how its distributed ledger model can replace middlemen and enable more open, trustworthy and secure digital record keeping through the use of techniques like smart contracts. The document presents several case studies of companies applying blockchain to improve IoT security for applications such as home rentals, solar energy tracking, and drone deliveries. It concludes by recommending some starting points for working with blockchain and IoT security, like the Ethereum platform.