This learning brief will explore experiences of water, sanitation and hygiene (WASH) system strengthening during the COVID-19 pandemic, through drawing on content from Hygiene Hub case studies and discussions with Hygiene Behaviour Change Coalition (HBCC) partners, as well as evidence and practice from numerous WASH and health stakeholders. We explore the different types of system strengthening activities implemented, common challenges encountered and key lessons and action points, before reflecting on cross-cutting challenges and lessons. This document, although drawing on WASH systems thinking, focusses primarily on water and hygiene. We also include two case studies from Amref and WaterAid which provide in-depth examples of system strengthening activities.