ISAS (In Situ Analysis System) is an analysis tool for producing gridded scalar fields. At the moment it is set to process temperature and salinity. Originally designed for the synthesis of ARGO dataset, it has been tested for the first time on the POMME area in the North-East Atlantic in 2000, it was later extended to the Atlantic and the Global ocean as the Argo array was setting up. It is developed and maintained at LPO (Laboratoire de Physique des Océans) within the Argo Observing Service (SO-ARGO) where it is used for research purposes on ocean variability. ISAS is made available to the Coriolis datacenter for exploitation in operational mode. The analysis is performed on the datasets prepared by Coriolis according to Argo recommendations for data quality control and NetCDF format. A set of background and statistical information required to complement the observations are provided with the software, as part of the configuration. For each analysis date, the results are provided in two NetCDF files, one holding the data and analysis residuals, the other holding the gridded fields and estimation error, expressed as percentage of a priori variance. This document describes how to implement the ISAS software. The main steps of the process are detailed and examples of configuration files are provided. The statistical method used to produce the estimate and the specific choices performed to implement the method are described in the Method and Configuration document corresponding to the appropriate ISAS version.