The smallest things known to man are particles called quarks and leptons, which are considered elementary particles. Quarks are fundamental constituents of protons and neutrons, which make up the atomic nucleus, while leptons include particles like electrons and neutrinos. These particles have no known substructure and are considered point-like, meaning they have no size or volume in the classical sense. They are typically described as point particles in particle physics. However, it's important to note that our understanding of the fundamental nature of particles is based on current scientific knowledge and may evolve with further discoveries and advancements in physics research.