Is there anything smaller than a quark?

Following the discovery of quarks inside protons and neutrons in the early 1970s, some theorists suggested quarks might themselves contain particles known as 'preons'. The idea wasn't entirely fanciful, but raises further, as-yet-unanswered questions; for the time being, most physicists believe that quarks, electrons and all other particles are best described as being vibrations of 'superstrings', multi-dimensional entities far smaller than the smallest sub-atomic particle.