  A broad overview of the current status of proton stability in unified models
of particle interactions is given which includes non - supersymmetric
unification, SUSY and SUGRA unified models, unification based on extra
dimensions, and string-M-theory models. The extra dimensional unification
includes 5D and 6D and universal extra dimensional (UED) models, and models
based on warped geometry. Proton stability in a wide array of string theory and
M theory models is reviewed. These include Calabi-Yau models, grand unified
models with Kac-Moody levels $k>1$, a new class of heterotic string models,
models based on intersecting D branes, and string landscape models. The
destabilizing effect of quantum gravity on the proton is discussed. The
possibility of testing grand unified models, models based on extra dimensions
and string-M-theory models via their distinctive modes is investigated. The
proposed next generation proton decay experiments, HyperK, UNO, MEMPHYS,
ICARUS, LANNDD (DUSEL), and LENA would shed significant light on the nature of
unification complementary to the physics at the LHC. Mathematical tools for the
computation of proton lifetime are given in the appendices. Prospects for the
future are discussed.
