  The study of $B \to \tau^+ \tau^- (X)$ decays can provide us with a better
understanding of the third generation, and can be a useful probe of physics
beyond the standard model. We present a model independent analysis of these
decays. We classify new physics that can largely enhance the decay rates and we
discuss the constraints implied by other processes. Experimentally, flavor
changing neutral current $B$ decays into final state $\tau$'s are still
unconstrained. Searches for $B$ decays with large missing energy at LEP provide
the first limits. We estimate that existing data already imply bounds on the
$B_d \to \tau^+ \tau^-$, $B_s \to \tau^+ \tau^-$, and $B \to X \tau^+ \tau^-$
decay rates at the few percent level. Although these bounds are over four
orders of magnitude above the standard model predictions, they provide the
first constraints on some leptoquarks, and on some R-parity violating
couplings.
