Sensus is an end-to-end system for mobile sensing using iOS and Android devices. Sensus is able to monitor a wide range of sensors and data events, and it is designed to interact with the user to solicit additional information via scheduled or sensor-triggered surveys. It coordinates the collection, anonymization, and storage of this information locally on the device and remotely on cloud servers. Sensus has been designed and implemented at the University of Virginia Predictive Technology Laboratory for research in public health and personal safety. However, Sensus is a general-purpose system. Researchers in other fields, industrial companies, and individuals interested in self-monitoring might find it useful.