Elementary particles are the most fundamental building blocks of the universe. Unlike atoms, which can be broken down into protons, neutrons, and electrons, elementary particles are indivisible—they have no known internal structure. These particles, governed by the principles of quantum mechanics, form the basis of all matter and energy interactions.

The concept of elementary particles has evolved over time. In ancient philosophy, matter was thought to be composed of indivisible units called "atoms," a term coined by the Greek philosopher Democritus. However, modern science has shown that atoms themselves are not fundamental, as they consist of smaller components. By the early 20th century, scientists had discovered the existence of protons, neutrons, and electrons, leading to the birth of particle physics as a discipline.

The real breakthrough in understanding elementary particles came with the development of quantum mechanics and relativity. In the 1920s and 1930s, physicists formulated quantum field theories that described how particles interact through fundamental forces. By the mid-20th century, experimental discoveries revealed that protons and neutrons were not fundamental but composed of even smaller particles called quarks. This led to the development of the Standard Model of Particle Physics, which remains the best theoretical framework for describing elementary particles and their interactions.