Matter is a term that traditionally refers to the substance that all objects are made of, though Aristotelian hylomorphism holds that matter is not necessarily a material category. The common way to identify this "substance" is through its physical properties; a common definition of matter is anything that has mass and occupies a volume. However, this definition has to be revised in light of quantum mechanics, where the concept of "having mass", and "occupying space" are not as well-defined as in everyday life. A more general view is that bodies are made of several substances, and the properties of matter (including mass and volume) are determined not only by the substances themselves, but by how they interact. In other words, matter is made up of interacting "building blocks", the so-called particulate theory of matter.

The concept of matter has been refined many times in history, in light of the improvement in knowledge of just what the basic building blocks are, and in how they interact. For example, in the early 18th century, Isaac Newton viewed matter as "solid, massy, hard, impenetrable, movable particles", which were "even so very hard as never to wear or break in pieces." The "primary" properties of matter were amenable to mathematical description, unlike "secondary" qualities such as color or taste. In the 19th century, following the development of the periodic table, and of atomic theory, atoms were seen as being the fundamental constituents of matter; atoms formed molecules and compounds.