  In this paper, we study the hyperbolicity of arborescent tangles and
arborescent links. We will explicitly determine all essential surfaces in
arborescent tangle complements with non-negative Euler characteristic, and show
that given an arborescent tangle T, the complement X(T) is non-hyperbolic if
and only if T is a rational tangle, T=Q_m * T' for some m greater than or equal
to 1, or T contains Qn for some n greater than or equal to 2. We use these
results to prove a theorem of Bonahon and Seibenmann which says that a large
arborescent link L is non-hyperbolic if and only if it contains Q2.
