SoC design challenges and opportunities for smart and secure cyberphysical systems in the world of Internet-of-Things (IoT) are presented, focusing on two distinct areas: (1) how to deliver uncompromising performance and user experience while minimizing energy consumption, and (2) how to provide cryptographic-quality “roots of trust” in silicon and resistance to physical side channel attacks with minimal overhead. SoC designs that span a wide range of performance and power across diverse platforms and workloads, and achieve robust near-threshold-voltage (NTV) operation in nanoscale CMOS, are discussed. Techniques to overcome the challenges posed by device parameter variations, supply noises, temperature excursions, aging-induced degradations, workload and activity changes, and reliability considerations are presented. True Random Number Generator (TRNG) and Physically Unclonable Function (PUF) circuits, the two critical silicon building blocks for generating dynamic and static entropy for encryption keys and digital fingerprints, respectively, are discussed. Power and electromagnetic physical side channel attack detection and mitigation techniques for enabling robust hardware security are also presented.