  Partons are effective degrees of freedom describing the structure of hadrons
involved in high-energy collisions. Familiar theories of partons are QCD
light-front quantization and soft-collinear effective theory, both of which are
intrinsically Minkowskian and appear unsuitable for classical Monte Carlo
simulations. A ``new'' form of the parton theory has been formulated in term of
the old-fashioned, Feynman's infinite momentum frame, in which the parton
degrees of freedom are filtered through infinite-momentum external states. The
partonic structure of hadrons is then related to the matrix elements of static
(equal-time) correlators in the state $|P^z=\infty\rangle$. This representation
lays the foundation of large-momentum effective theory (LaMET) which
approximates parton physics through a systematic $M/P^z$ expansion of the
lattice QCD matrix elements at a finite but large momentum $P^z$, and removes
the residual logarithmic-$P^z$ dependence by the standard
effective-field-theory matching and running.
