During a volcanic effusive crisis, the active lava flow(s) need(s) to be monitored to best anticipate the possible affected area. A number of measurements needs to be made on site either from ground or from the air and by satellite imagery. These measurements need to be made through established protocols so derivative parameters can be calculated and extracted to contribute to forecasting and reduce possible impacts of lava flows. Measurements and reporting parameters include lava flow setting, morphological description, dimensions (thickness, length, width, underlying slope), temperature (core and surface), and sampling. First order derivative are topographical changes, estimation of emitted lava volume, lava flow velocity (channel and front), cooling rate, petrology and lava flow type characteristics. Second order derivative then involve volumetric discharge rate estimation, heat budget models and rheological constrains. These are essential parameters that are part of the monitoring duties and feed lava flow hazard projection and numerical modelling. In this chapter, we review the measurements that are typically made and the subsequent derivatives that all contribute to monitoring activities during an effusive event.