Chronic diseases are costly for global health systems and society in general. Many of the associated health problems can be prevented by adherence to healthy lifestyle. This book undertakes the design and evaluation of a behaviour analysis and reminder delivery framework, referred as iMessenger, which comprises four topics: activity classification; location detection; context management; and reminder delivery. The activity classification module extracted the activity postures using an accelerometer embedded in a belt-worn smart phone. The location detection module localized tagged subjects based on RFID technologies. Ontological modeling and reasoning were utilized to integrate heterogeneous contexts, and to infer users’ current activity and situations. The inference results were generated into situation-aware reminders. iMessenger has the potential to encourage people to adopt a healthier lifestyle for enhanced well-being and can therefore potentially reduce the burden of healthcare. This book should be useful to professionals in healthcare and smart home fields, or anyone else who may be interested in these research areas.