In a nutshell, Phase 3 denotes the process of preparation, validation and ingestion of science data products (SDPs) for storage in the ESO science archive facility, and subsequent data publication to the scientific community. SDPs are data products with instrument and atmospheric signatures removed, calibrated in physical units, with noise properties (like limiting magnitude or signal-to-noise ratio) quantified and documented. SDPs are produced by:

• principal investigators (PIs) of ESO observing programmes primarily from ESO public surveys, large programmes and calibration programmes,
• ESO scientists using the ESO pipelines as part of the quality control (QC) process or from specific, dedicated, re-processing projects for homogenous raw data sets,
• users of non-ESO telescopes such as GTC, NGTS, etc
• PIs of ESO normal programmes on voluntary basis,
• members of the community interested in publishing data from archival research.

ESO’s policies governing Phase 3 are specific to the type of observing programme. Phase 3 is mandatory for ESO Public Surveys and for ESO Large Programmes since period 75. For other ESO programmes there is no obligation but PIs are invited to take advantage of the Phase 3.

To ensure the successful integration of SDPs into the archive, ESO supports the users in carrying out the Phase 3 process by defining ESO/SDP data standards, by devising procedures and providing the infrastructure for the delivery of SDPs, and by supplying tools for the data preparation.

The description of the policies, the data standard and the procedure for the submission of reduced data products applicable to the ESO Phase 3 process given here is intended to provide the information for the preparation and successful completion of the ESO Phase 3 process.

The target audience consists of 1) principal investigators and their collaborators who return reduced data products resulting from ESO/non-ESO observations for public release to the astronomical community through the ESO archive, 2) ESO scientists involved in the QC process or in specific re-processing projects, 3) instruments scientists and pipeline developers for the new and existing ESO instruments, 4) archive users who need to understand the structure and format of the SDPs they intend to use for their own science.