Kaṇāda (Sanskrit: कणाद, romanized: Kaṇāda), also known as Ulūka, Kashyapa, Kaṇabhaksha, Kaṇabhuj was an ancient Indian natural scientist and philosopher who founded the Vaisheshika school of Indian philosophy that also represents the earliest Indian physics.

Estimated to have lived sometime between 6th century to 2nd century BCE, little is known about his life. His traditional name "Kaṇāda" means "atom eater", and he is known for developing the foundations of an atomistic approach to physics and philosophy in the Sanskrit text Vaiśeṣika Sūtra. His text is also known as Kaṇāda Sutras, or Aphorisms of Kaṇāda.

The school founded by Kaṇāda explains the creation and existence of the universe by proposing an atomistic theory, applying logic and realism, and is one of the earliest known systematic realist ontology in human history. Kaṇāda suggested that everything can be subdivided, but this subdivision cannot go on forever, and there must be smallest entities (paramanu) that cannot be divided, that are eternal, that aggregate in different ways to yield complex substances and bodies with unique identity, a process that involves heat, and this is the basis for all material existence. He used these ideas with the concept of Atman (soul, Self) to develop a non-theistic means to moksha. If viewed from the prism of physics, his ideas imply a clear role for the observer as independent of the system being studied. Kaṇāda's ideas were influential on other schools of Hinduism, and over its history became closely associated with the Nyaya school of Hindu philosophy.

Kaṇāda's system speaks of six properties (padārthas) that are nameable and knowable. He claims that these are sufficient to describe everything in the universe, including observers. These six categories are dravya (substance), guna (quality), karmana (motion), samaya (time), visesa (particular), and samavaya (inherence). There are nine classes of substances (dravya), some of which are atomic, some non-atomic, and others that are all-pervasive.

The ideas of Kaṇāda span a wide range of fields, and they influenced not only philosophy, but possibly scholars in other fields such as Charaka who wrote a medical text that has survived as Charaka Samhita.