Resilient monitoring systems (RMS) are sensor networks that degrade gracefully under malicious attacks on their sensors, causing them to project misleading information. This paper develops techniques to ensure resiliency, namely: active data quality acquisition, process variable and plant condition assessments, sensor network adaptation, and plant decomposition with knowledge fusion. Based on these techniques, we design a RMS for power plants and investigate its performance under various cyber-physical attacks. In all scenarios considered, the system offers effective protection against misleading information and identifies the plant condition - normal or anomalous - in a reliable and timely manner. (C) 2015 Elsevier Ltd. All rights reserved.