This week we study hardware Trojan and trusted integrated circuit (IC) design. Hardware Trojans are additions or modifications of the circuit with malicious purposes. It has become one of the most dangerous and challenging threats for trusted ID design. We will give hardware Trojan taxonomies based on different criteria, explain how hardware Trojan work, and then talk about some of the existing approaches to detect them. We define trusted IC as circuit that does exactly what it is asked for, no less and no malicious more. We will illustrate this concept through the design space analysis and we will discuss several practical hardware Trojan prevention methods that can facilitate trust IC design.