  We present a microscopic theory for superfluidity in an interacting
many-particle Bose system (such as liquid $^4$He). We show that, similar to
superconductivity in superconductors, superfluidity in a Bose system arises
from pairing of particles of opposite momenta. We show the existence of an
energy gap in single-particle excitation spectrum in the superfluid state and
the existence of a specific heat jump at the superfluid transition. We derive
an expression for superfluid particle density $n_s$ as a function of
temperature $T$ and superfluid velocity ${\bf v}_s$. We show that
superfluid-state free energy density $F$ is an increasing function of $v_s$
(i.e., $\partial F/\partial v_s > 0$), which indicates that a superfluid has a
tendency to remain motionless (this result qualitatively explains the
Hess-Fairbank effect, which is analogous to the Meissner effect in
superconductors). We further speculate the existence of the equation ${\bf
j}=-\Lambda\nabla\times \text{\boldmath $\omega$}$, where ${\bf j} = n_s{\bf
v}_s$ is the superfluid current density, $\text{\boldmath
$\omega$}=\nabla\times {\bf v}_s$ the superfluid vorticity, and $\Lambda$ a
positive constant (with the help of this equation, the Hess-Fairbank effect can
be quantitatively described).
