The mechanism of the electroweak symmetry-breaking (EWSB) is studied in the
context of the heavy top quark, whose large mass may provide a clue as to the
mechanism which generates the mass of the $W^\pm$ and $Z$ bosons. As a result,
it seems quite likely that the top quark may be special in the sense that it is
involved in dynamics not experienced by the light fermions. Examples of this
include models such as the top-condensate model in which a bound state of top
quarks condenses, generating both the top mass and the gauge boson masses, and
supersymmetric models in which the large top Yukawa coupling naturally explains
the EWSB by radiatively driving the squared mass of a scalar particle (which is
positive at a large energy scale) negative at low energies. Specific collider
signatures of the third family result from such scenarios, and can be used to
test the hypothesis that the top plays a role in the EWSB. In particular,
single top production, as a measure of the top's weak interactions, provides an
excellent probe of nonstandard top quark properties. The physics of single top
production at hadron colliders is carefully studied, with a particular eye
towards what can be learned from single top, including the signs of new physics
that may show up in the single top rate.