  I survey a number of interesting tests of quantum chromodynamics at the
amplitude level which can be carried out in electron-positron annihilation and
in photon-photon collisions at low energy, including measurements of
fundamental processes such as timelike form factors and transition amplitudes,
timelike Compton scattering, timelike photon to meson transition amplitudes,
and two-photon exclusive processes. Many of these reactions test basic
principles of QCD such as hadronization at the amplitude level, factorization,
and hadron helicity conservation, tools also used in the analysis of exclusive
$B$ and $D$ decays. Measurements of the final-state polarization in hadron pair
production determine the relative phase of the timelike form factors. The role
of two-photon exchange amplitudes can be tested using the charge asymmetry of
the $e^+ e^- \to B \bar B$ processes. Precision measurements of the
electron-positron annihilation cross section can test the generalized Crewther
relation and determine whether the effective couplings defined from physical
measurements show infrared fixed-point and near conformal behavior. I also
discuss a number of tests of novel QCD phenomena accessible in $e^+ e^-$
annihilation, including near-threshold reactions, the production of baryonium,
gluonium states, and pentaquarks.
