The Kingdom of Kotte (Sinhala: කෝට්ටේ රාජධානිය, romanized: Kōṭṭē Rajadhaniya, Tamil: கோட்டை அரசு), named after its capital, Kotte, was a Sinhalese kingdom that flourished in Sri Lanka during the 15th century.

Founded by Parakramabahu VI with the help of the Ming, the Kingdom managed to conquer the Jaffna kingdom and the Vanni principalities, and bring the country under one flag. It led to a punitive invasion against the Vijayanagar dynasty and captured a port.

The Kotte Kingdom was largely dissolved during the Sinhalese-Portuguese War, as it faced attacks from rival Sinhalese kingdoms , the Kingdom of Sitawaka and Kingdom of Kandy. Dom João Dharmapala handed it over to the Portuguese, thus leading to the formation of Portuguese Ceylon. Kanakasooriya Cinkaiariyan and his two son's also returned from Madurai with mercenaries and managed to conquer Jaffna. The remainder was annexed into Sitawaka and Kandy.

The term Kotte is said to have derived from the Sinhalese word kōṭṭa (කෝට්ට) meaning “fortress,” which itself is thought to have originated from the Tamil word kōṭṭai. The word Kotte was introduced by Nissankamalla Alagakkonara, who was the founder of the fortress. They were believed to be from the city of Vanchi, identified with Kanchipuram of Tamil Nadu. The Alagakkonara family have also been identified to be of Tamil ancestry of Vallanattu Chettiar.

Kotte was originally founded as a fortress by Minister Alakesvara (1370–1385) of the Alagakkonara clan in the Kingdom of Gampola during the reign of Vikramabahu III of Gampola. It was built to counter invasions from South India along the western coast.

In 1412, Parakramabahu VI established Kotte as his capital city. The site was naturally well protected by the extensive swamp that surrounded it.^{[failed verification]}

Parakramabahu VI first became the king of Gampola in 1412, and in 1415, he established Kotte as his capital. He expanded and fortified the existing citadel and built a new royal palace. Parakramabahu VI waited until ties between the Vijayanagara Empire and Jaffna Kingdom were severed. First, he captured the Vanni and made its leaders loyal to him. Prince Sapumal was the commander of the Kotte army at the time. However, Kanakasooriya Cinkaiariyan and his two sons soon returned from Madurai with mercenaries and regained control of the Jaffna Kingdom, bringing it out of Kotte’s overlordship and reestablishing its independence. During this period, Tamil was used as one of the court languages of the Kotte Kingdom.

In 1450, through his conquest of the Jaffna Kingdom in northern Sri Lanka, Parakramabahu VI succeeded in unifying the entire island under his rule. At its height, the Kingdom oversaw one of the greatest eras of Sinhalese literature. Notable poets at the time were Buddhist monks such as Thotagamuwe Sri Rahula thero, Weedagama Maithree thero, and Karagala Wanarathana thero. By 1477, a decade after the death of Parakramabahu VI, regional kingdoms had grown in strength. Most notably a new Kingdom was founded in the central hill country of the island by Senasammata Vikramabahu who successfully led a rebellion against the Kotte Kingdom in 1469.