Kaundinya (Sanskrit कौंडिन्य), also known as Ājñātakauṇḍinya, Pali: Añña Koṇḍañña), was one of the first five Buddhist monks (Pancavaggiya), disciple of Gautama Buddha and the first to attain the fruit of Arahant. He lived during the 5th century BCE in what are now Uttar Pradesh and Bihar, India. According to traditional accounts, at the time of Gautama Buddha's birth, he predicted his future destination as an enlightened teacher.

Kaundinya first came to prominence as a royal court scholar of King Suddhodana of the Sakyas in Kapilavastu. There Kaundinya was the only scholar who unequivocally predicted upon the birth of Prince Siddhartha that the prince would become an enlightened Buddha, and vowed to become his disciple. Kaundinya and four colleagues followed Siddhartha in six years of ascetic practice, but abandoned him in disgust after Siddhartha gave up the practice of self-mortification. Upon enlightenment, Siddhartha gave his first Dhamma talk or sermon to Kaundinya's group. Kaundinya was the first to comprehend the teaching and thus became the first bhikkhu and arahant.

Kaundinya was aware as the foremost of the five initial disciples of the Buddha and later travelled around India spreading the dharma. Among his notable converts was his nephew Puṇṇa, who the Buddha acknowledged as the foremost preacher of the Dhamma. In his final years, he retreated to the Himalayas and predeceased the Buddha.

Kaundinya's previous rebirths are described in many accounts in Buddhist literature. These accounts show that he had vowed in previous existences to be the first to comprehend the dharma when it was to be proclaimed by an enlightened Buddha. They also document that the seeds of his relationship with Gautama Buddha as the first arahant were sown in previous existences in which they had crossed paths.

Kaundinya was born before the time of Siddhartha to a wealthy family in a town named in hassan, near Kapilavastu, and was known by his family name. When he was growing up, he mastered the three Vedas at a young age and excelled in the science of physiognomy (lakhana-manta).

Kaundinya became a young Brahmin scholar in Kapilavastu in the Sakya kingdom of King Suddhodana. He was one among the group of scholars who were invited to the royal court to predict the destiny of Crown Prince Siddhartha at his naming ceremony. Siddhartha was the first child born to Suddhodana and Queen Maya in twenty years of marriage and much interest surrounded the infant from royal society and the public alike. All the other scholars raised two fingers and offered a twofold prediction: That Siddhartha would either become a Chakravarti (supreme king) or would renounce the world and become a supreme religious leader. Kaundinya was the only one that explicitly predicted that Siddhartha would renounce the world to become a Buddha, raising one finger and stating his prediction.

Kaundinya thereafter vowed that he would follow when Siddhartha became an ascetic to learn from the future Buddha's findings. In the meantime, Suddhodana attempted to foil Kaundinya's prediction because he wanted his son to succeed him in ruling and expanding the kingdom. Suddhodana made intricate arrangements to shield Siddhartha from all worldly suffering in order to steer his mind away from spiritual matters, pampering him with all the material luxury and sense pleasures that he could find. However, Siddhartha finally persuaded his father to allow him out of the palace to meet his subjects. Suddhodana agreed, but attempted to present a sanitised image of human existence by ordering beggars, old people and sick people to be kept from the streets. Despite this, Siddhartha saw the four sights which prompted him to reevaluate his view of the world.

When Siddhartha was aged 29, he renounced the world to become a samaṇa (ascetic). Kaundinya, along with Bhaddiya, Vappa, Mahanama and Assaji, variously described as four of the other scholars who had read Siddhartha's future or the sons of those scholars, followed him into the ascetic life, with the approval of Suddhodana, who was worried about Siddhartha's safety. They were known as "the group of five" or "the group of five fortunate ones". After Siddhartha had mastered all the teachings of Āḷāra Kālāma and then Uddaka Rāmaputta, he left and began practicing self mortification along with Kaundinya and his four colleagues at Uruvela. Kaundinya and his colleagues attended to Siddhartha in the hope that he would become enlightened through self-mortification. These involved self-deprivation of food and water, and exposing themselves to the elements to near-death for six years, at which point Siddhartha rejected self-mortification. Kaundinya and his colleagues became disillusioned, believing Siddhartha to have become a glutton and moved away to Sarnath near Varanasi to continue their practices.