Physics at a future e+e- collider

The European Strategy for Particle Physics identified an high-energy e+e-
collider studying the Higgs boson as the
next priority collider project. The different proposals to realize such a
collider all reach a similar performance on the core Higgs
program at 250 GeV, albeit with different choices of luminosity and
polarisation - but they differ in capabilities at lower and higher energies.
This talk will review the physics capabilities of future e+e- colliders in
the Higgs sector and beyond, with a specific emphasis illuminating
the interplay of the top-level beam parameters luminosity, energy and
polarisation.