This Product User Guide (PUG) provides the specifications of the ESA CCI Soil Moisture (SM) v08.1 product. The targeted audience of this document is mainly the product users. The ESA CCI SM v08.1 product consists of three surface soil moisture data sets: The “ACTIVE Product” and the “PASSIVE Product” were created by fusing scatterometer and radiometer soil moisture products, respectively; The “COMBINED Product” is a blended product based on the former two data sets. Data files are provided as NetCDF-4 classic format and comprise global merged surface soil moisture datasets at daily temporal resolution. The data set spans over 40 years covering the period from November 1978 to December 31st 2022. This document forms the deliverable D4.2 Version 1, Product Users Guide (PUG) and was compiled for the European Space Agency (ESA) Climate Change Initiative Plus Soil Moisture Project (ESRIN Contract No: 4000126684/19/I-NB: ”ESA CCI+ Phase 1 New R&D on CCI ECVS Soil Moisture”). This document supports CCI SM product version v08.1