  The conductance of a ballistic quantum dot (having chaotic classical dynamics
and being coupled by ballistic point contacts to two electron reservoirs) is
computed on the single assumption that its scattering matrix is a member of
Dyson's circular ensemble. General formulas are obtained for the mean and
variance of transport properties in the orthogonal (beta=1), unitary (beta=2),
and symplectic (beta=4) symmetry class. Applications include universal
conductance fluctuations, weak localization, sub-Poissonian shot noise, and
normal-metal-superconductor junctions. The complete distribution P(g) of the
conductance g is computed for the case that the coupling to the reservoirs
occurs via two quantum point contacts with a single transmitted channel. The
result P(g)=g^(-1+beta/2) is qualitatively different in the three symmetry
classes. ***Submitted to Europhysics Letters.****
