RF MEMS switches and varactors are the conventional devices commonly employed to tune the response of a large variety of circuits and antennas. Despite their many advantages, important limitations still exist today in consistently building reliable MEMS structures, high-performance reconfigurable circuits, and robust harsh-environment micro-sensors. The market volume of RF MEMS does not favor multi-billion dollar foundries that are often the norm for CMOS and SiGe technologies. Consequently, process uncertainty becomes a critical issue with few solutions being available today. Such limitations have significantly slowed down the adoption of RF MEMS in commercial products and defense systems. In this seminar we will present new promising methods for addressing many of these challenges. In these methods we seek solutions at the fabrication technology, device, and sub-system levels. As an example, we will present a unique three-dimensional architecture for obtaining base-station quality tunable microwave filters in mobile form factors. These filters simultaneously exhibit a very wide tuning range (>2:1) and a very high quality factor (Q~1,000) at 6 GHz. In addition, they show orders of magnitude improved performance with respect to creep compared to conventional RF MEMS structures. Besides MEMS for RF systems, we will also discuss inherently-reliable harsh-environment MEMS sensors for the health monitoring of aircraft engines. These sensors have demonstrated reliable operation up to 300 degrees C and have successfully identified operating condition changes when attached to ball/roller bearings rotating up to 50,000 rpm. These approaches constitute a paradigm shift on existing RF MEMS practices and provide a path for addressing some of the remaining critical MEMS issues.