  The European Solar Telescope (EST) is a research infrastructure for solar
physics. It is planned to be an on-axis solar telescope with an aperture of 4 m
and equipped with an innovative suite of spectro-polarimetric and imaging
post-focus instrumentation. The EST project was initiated and is driven by
EAST, the European Association for Solar Telescopes. EAST was founded in 2006
as an association of 14 European countries. Today, as of December 2019, EAST
consists of 26 European research institutes from 18 European countries.
  The Preliminary Design Phase of EST was accomplished between 2008 and 2011.
During this phase, in 2010, the first version of the EST Science Requirement
Document (SRD) was published. After EST became a project on the ESFRI roadmap
2016, the preparatory phase started. The goal of the preparatory phase is to
accomplish a final design for the telescope and the legal governance structure
of EST. A major milestone on this path is to revisit and update the Science
Requirement Document (SRD).
  The EST Science Advisory Group (SAG) has been constituted by EAST and the
Board of the PRE-EST EU project in November 2017 and has been charged with the
task of providing with a final statement on the science requirements for EST.
Based on the conceptual design, the SRD update takes into account recent
technical and scientific developments, to ensure that EST provides significant
advancement beyond the current state-of-the-art.
  The present update of the EST SRD has been developed and discussed during a
series of EST SAG meetings. The SRD develops the top-level science objectives
of EST into individual science cases. Identifying critical science requirements
is one of its main goals. Those requirements will define the capabilities of
EST and the post-focus instrument suite. The technical requirements for the
final design of EST will be derived from the SRD.
