  Understanding the internal spin structure of the nucleon remains a challenge
in strong interaction physics. The unique capability of RHIC opened new avenues
in studying the internal structure of the proton with unprecedented depth and
precision. Significant progress has been made in the last few years through
various measurements at STAR. The longitudinal spin measurements have
contributed significantly to our understanding of the quark and gluon helicity
distributions inside the proton. The longitudinal double-spin asymmetry,
$A_{LL}$, from STAR inclusive jet and dijet measurements provides the first
evidence of a positive gluon polarization with partonic momentum fraction $x >
0.05$. The reconstruction of $W^{\pm}/Z$ in longitudinally polarized
proton-proton collisions indicates that there is a flavor separation of the
light sea quark helicity distributions. In transversely polarized proton
collisions, $W^{\pm}/Z$-bosons provide the first constraint on the sea-quark
Sivers function and contributes to the tests of the predicted sign change. The
tilt of the dijet opening angle provides a direct access to the first Mellin
momentum of the Sivers function and avoids the spin-correlated fragmentation
contributions. The novel measurements of the azimuthal distributions of
identified hadrons in jets and spin-dependent dihadron correlations directly
probe the collinear quark transversity in the proton, with the former coupled
to the transverse momentum dependent (TMD) Collins fragmentation function and
the latter to the dihadron interference fragmentation function. These
measurements shed lights on Sivers function, quark transversity and
spin-dependent fragmentation functions in both collinear and TMD formalism. In
this proceeding, recent jet results on both the longitudinal and transverse
spin structure of the proton from STAR are presented.
