Insect pest monitoring serves to evaluate pest severity over time and space. Special attention is given to acquiring and estimating pest population levels and affiliated variables that may influence trajectory of pest severity within and across crops and other habitat. The chapter reviews approaches and provides case studies of current advances that are in development or have been applied in operational integrated pest management (IPM) systems. We first review incorporating knowledge of expected pest population growth to adjust economic thresholds for use in applying remedial IPM tactics to individual fields. The chapter then turns to principles and advancements in using spatial data, including spatially-referenced pest, crop, and remote sensing data. Spatial data linked to insect pest monitoring may improve strategic use of remedial IPM tactics at the field level and use of preventive IPM tactics at larger scales.