  Large dimensionless numbers, arising out of ratios of various physical
constants, intrigued many scientists, especially Dirac. Relying on the
coincidence of large numbers, Dirac arrived at the revolutionary hypothesis
that the gravitational constant $G$ should vary inversely as the cosmic time
$t$. This hypothesis of Dirac, known as Large Number Hypothesis (LNH), sparked
off many speculations, arguments and new ideas in terms of applications. Works
done by several authors with LNH as their basic platform are reviewed in this
work. Relationship between some of those works are pointed out here.
Possibility of time-variations of physical constants other than $G$ are also
discussed.
