  We report a record high superconducting transition temperature ($T_{\rm c}$)
up to 23.6 K under high pressure in the elemental metal Ti, one of the top ten
most abundant elements in Earth's crust. The $T_{\rm c}$ increases
monotonically from 2.3 K at 40.3 GPa to 23.6 K at 144.9 GPa, which surpasses
all known records from elemental metals reported so far. With further
compression, a robust $T_{\rm c}$ of ~23 K is observed between 144.9 and 183
GPa in the $\delta$-Ti phase. The pressure-dependent $T_{\rm c}$ can be well
described by the conventional electron-phonon coupling (EPC) mechanism. Density
Functional Theory calculations show the Fermi nesting and the phonon softening
of optical branches at the $\gamma$-Ti to $\delta$-Ti phase transition pressure
enhance EPC, which results in the record high $T_{\rm c}$. We attribute the
robust superconductivity in $\delta$-Ti to the apparent robustness of its
strong EPC against lattice compression. These results provide new insight into
exploring new high-$T_{\rm c}$ elemental metals and Ti-based superconducting
alloys.
