This document serves as a summary of the work of Subgroup 20 (SG20) on covariance matrix evaluation and processing in the resolved/unresolved resonance regions, organised under the auspices of the NEA's Nuclear Science Committee Working Party on International Evaluation Co-operation (WPEC).
The work described in this report focuses on: summarising the issues related to covariance evaluation in the resonance region; discussing the retroactive method used in the SAMMY code; describing the compact format for storing huge covariance matrices in ENDF-6 files; recent developments and upgrades of processing codes to generate a multi-group covariance matrix from resonance parameter covariance data.