T h e last thirt y years hav e see n a n enormou s advanc e i n
o u r understandin g o f th e microscopi c world . W e no w
hav e a convincin g pictur e o f th e fundamenta l struc -
tur e o f observabl e matte r i n term s o f certai n point-lik e
elementar y particles. W e als o hav e a comprehensiv e
theor y describin g th e behaviou r o f an d th e force s
betwee n thes e elementar y particles, whic h w e believ e
provide s a complet e an d correc t descriptio n o f nearl y
a l l non-gravitationa l physics.