Recently, ubiquitous location-based services (u-LBS) has been utilized in a variety of practical and mission-critical applications such as security services, personalization services, location-based entertainment, and location-based commerce. The essence of u-LBS is actually the concept of location-awareness where location-aware devices perform more intelligent services for users by utilizing their locations. In order to realize/achieve this concept, a mobile device should continuously monitor the real-time contextual changes of a user; this is what we call locationbased monitoring. In this paper, we discuss the research and technical issues on designing location-based real-time monitoring systems in uLBS along with three major subjects: (1) high-performance spatial index, (2) monitoring query processing engine, and (3) distributed monitoring system with dynamic load balancing capability and energy-efficient management.