The top quark os a most remarkable Particle even for a quark. A single “top,” as we will casually call it here, weighs 175 GeV, about as much as an atom of gold. But unlike the gold atom, which can be disassembled into 79 protons, 79 electrons and 118 neutrons, top seems to be indivisible. With an experimental resolution approaching10−16 cm,we have not discerned any structure. Top's predicted lifetime of about 0.4 yoctoseconds(0.4×10−24 s)makes it by far the most ephemeral of the six varieties of quarks. The compensation for this exceedingly brief life is a measure of freedom: Top decays before it suffers the confining influence of the strong interactions. In spite of its fleeting existence, the top quark nonetheless helps shape the character of the everyday world.