Wireless sensor networks, which represent a basic tenet of what we call ubiquitous computing, are now or will soon be deployed in physical environments that are vulnerable not only to the vicissitudes of nature but also to acts that could be easily viewed as hostile attacks by potent adversaries. Indeed, unattended operation of sensor-network nodes in hostile environments requires that we rethink the definition of “adversary”, as well as its capabilities and modes of attack. There are few problems of wireless sensor network design and analysis that are as challenging as localization and time synchronization. Yet both are fundamental building blocks not just for new applications and but also security services themselves. The natural interplay between space and time measurements and bounds, which are basic to both localization and time synchronization, produces a largely uncharted research territory. And, of course, the new capabilities and attack modes of the new adversary complicates the landscape in unanticipated ways. We developed robust location estimation approach called SeRLoc for wireless sensor networks that need to operate in hostile environments. We also developed a high resolution version of the localization. This work eventually led to technology now used by the U.S. Navy. We also organized a workshop and edited a book in this area. Applications of secure location estimation include relative location estimation, building and infrastructure health monitoring, and location verification in cognitive radios.