  Einstein's celebrated theory of gravitation can be presented in three forms:
general relativity, teleparallel gravity, and the rarely considered before
symmetric teleparallel gravity. Extending the latter, we introduce a new class
of theories where a scalar field is coupled nonminimally to nonmetricity $Q$,
which here encodes the gravitational effects like curvature $R$ in general
relativity or torsion $T$ in teleparallel gravity. We point out the
similarities and differences with analogous scalar-curvature and scalar-torsion
theories by discussing the field equations, role of connection, conformal
transformations, relation to $f(Q)$ theory, and cosmology. The equations for
spatially flat universe coincide with those of teleparallel dark energy, thus
allowing to explain accelerating expansion.
