  We explore the statistical properties of grain boundaries in the vortex
polycrystalline phase of type II superconductors. Treating grain boundaries as
arrays of dislocations interacting through linear elasticity, we show that
self-interaction of a deformed grain boundary is equivalent to a non-local
long-range surface tension. This affects the pinning properties of grain
boundaries, that are found to be less rough than isolated dislocations. The
presence of grain boundaries has an important effect on the transport
properties of type II superconductors as we show by numerical simulations: our
results indicate that the critical current is higher for a vortex polycrystal
than for a regular vortex lattice. Finally, we discuss the possible role of
grain boundaries in vortex lattice melting. Through a phenomenological theory
we show that melting can be preceded by an intermediate polycrystalline phase.
