Chapter 1 provides an overview of the globalized IC supply and the associated threats. It emphasizes the necessity of IC-based systems in critical infrastructure and describes different types of security threats and the latest countermeasures. The chapter also examines the shortcomings of these countermeasures while highlighting the need for ReBO as a solution. ICs play a vital role in various electronic systems, from household devices and mobile phones to military equipment and satellites. Over time, hardware security has become increasingly significant, especially due to the rise of specialized attacks. The globalization of the IC supply chain has allowed for profit-driven hardware-based attacks such as reverse engineering and IP piracy. Although multiple security measures have been introduced to protect a chip’s IP throughout the many steps of the IC supply chain and the IC design flow, they are often targeted by attacks. This chapter then introduces a new approach called “ReBO” as a countermeasure against various hardware-based attacks. In essence, ReBO conceals the functionality of a design until it is programmed with a bitstream.