  The properties of the interstellar medium (ISM) of the highest-redshift
galaxies and quasars provide important indications of the complex interplay
between the accretion of baryons onto galaxies, the physics that drives the
build-up of stars out of this gas, the subsequent chemical evolution and
feedback processes and the reionisation of the Universe. The Atacama Large
Millimeter/submillimeter Array (ALMA) continues to play a pivotal role in the
characterisation of the ISM of high-redshift galaxies. Observations of the dust
continuum emission, atomic fine-structure and molecular lines arising from
high-redshift galaxies are now carried out routinely, providing ever more
constraints on the theoretical models of galaxy formation and evolution in the
early Universe. The European Astronomical Society's EAS 2021 symposium
dedicated to the exploration of the high-redshift Universe with ALMA provided a
forum for the observational and theoretical high-redshift ALMA communities to
exchange their views and recent results in this rapidly evolving field. The
article summarises the exciting results that were presented at the meeting.
