Pre-Town Meeting on spin physics at an Electron-Ion Collider

. A polarized ep / eA collider (Electron-Ion Collider, or EIC), with polarized proton and light-ion beams and unpolarized heavy-ion beams with a variable center-of-mass energy √(s)∼ 20 to ∼ 100 GeV (upgradable to ∼ 150 GeV) and a luminosity up to ∼ 10^34 cm -2 s -1 , would be uniquely suited to address several outstanding questions of Quantum Chromodynamics, and thereby lead to new qualitative and quantitative information on the microscopic structure of hadrons and nuclei. During this meeting at Jefferson Lab we addressed recent theoretical and experimental developments in the spin and the three-dimensional structure of the nucleon (sea quark and gluon spatial distributions, orbital motion, polarization, and their correlations). This mini-review contains a short update on progress in these areas since the EIC White paper (A. Accardi et al. , Eur. Phys. J. A 52 , 268 (2016)).