The Vajjika (Pāli: Vajjika) or Vrijika (IAST: Vṛjika) League, Confederacy, or Sangha, also called simply Vajji (Pāli: Vajji) or Vriji (IAST: Vṛji), was an ancient Indo-Aryan tribal league which existed during the later Iron Age period in north-east India.

The Vajjika League was named after one of its constituent tribes, the Vajjikas proper, who had once been the most powerful tribe in the region of the league's capital of Vesālī. The larger region of the former Mahā-Videha kingdom in which the Vajjika League was located was in turn named after the confederacy.

According to Chinese pilgrim Xuanzang, the name Saṃvajji, meaning "united Vajjis," was given by the peoples of northern South Asia to the Vajjika League.

The Vajjika League was a league of republican tribal states under the leadership of the Licchavikas centred around the city of Vesālī. The other members of the league were the Vaidehas in the Mithila region, the Nāyikas of Kuṇḍapura, and the Vajji tribe proper, who were dependencies of the Licchavikas. The Mallakas, who were organised into two separate republics, were also part of the Vajjika League, although they were not dependencies of the Licchavikas and therefore maintained their independence and sovereign rights within the confederation, hence why Jain sources considered the Licchavikas and the neighbouring Mallakas of Kusinārā and Pāvā to be the republican states of Kāsī-Kosala.

The once popular view among scholars that the Vajjika League was constituted of eight clans was based on a misreading of the 5th century CE Buddhist commentator Buddhaghosa's mention that the legal tribunals of Vesālī included the aṭṭhakulika (अट्ठकुलिक), which was interpreted as meaning "eight tribes." The Pāli term kula (कुल) however means "clan" while the word for "tribe" is jana (जन), meaning that the term aṭṭhakulika instead referred to the heads of the eight leading ruling families of Vaisali and not to eight tribes.

The Vajjika League was administered by the Vajjika Council, which consisted of eighteen members, of which nine were from the confederacy's leading Licchavika tribe while the other nine members were from the Videha, Nāya, Vajji, and Malla tribes.

Since the Licchavikas were the leading tribe of the confederacy, their capital city of Vesālī was the headquarter of the Vajjika League, and their army also functioned as the Vajjika army, although the other confederated tribes were also required to furnish troops to the league.

The area of the Vajjika League was bounded to the north, east, south, and west, respectively, by the Himālaya mountains, and the Mahānanda, Gaṅgā, and Sadānirā rivers.