Several meteorological variables need to be measured at ICOS monitoring stations in order to characterize them, analyse the drivers explaining GHG fluxes, and properly calculate, partition and aggregate these fluxes and their seasonal budgets from eddy covariance (EC) measurements, the storage profile, automatic chambers, etc. This Instruction document deals with all the relevant air characteristics to be measured at ICOS stations, i.e. air temperature (TA), air relative humidity (RH), air pressure (PA), wind speed (WS) and wind direction (WD). Radiations and Precipitations are kept separated in dedicated documents. Furthermore, in order to reduce the occurrence of gaps in meteorological data and to have a reference, ICOS stations have to be equipped with a backup meteorological station in the vicinity of the main one. The steps needed to install, maintain, calibrate the sensors, up to the data collection, processing and submission are described in this Instruction document for the meteorological variables. For the sensors in the backup station that are not described in the present document, the respective Instruction documents must be consulted. The info are contained in the following sections: - Measurements: in this section the sensors are described, and the steps to perform from the installation to the data collection are illustrated. - Maintenance and calibration: in this section all the maintenance and calibration guidelines are described, including the general timeline and how to deal with repairs. - Submission: it is the section related to the data preparation and submission to the ETC. It includes a summary of the submission workflow described in a dedicated document, and lists all metadata and ancillary parameters to be sent to the ETC, and how to submit them. - Processing: this section is for internal use of the ETC and describes the processing applied to the single variable/info/sample submitted. It is important to remind that the exact application of the protocol at station level must be also discussed with the ETC in order to reach agreed solutions for specific cases. If a specific part is relevant only for a specific ecosystem or site Class this is also reported in the document.