Shugendō (修験道, lit. 'the "Way [of] Trial [and] Practice", the "Way of Shugen, or Gen-practice"') is a syncretic Esoteric Buddhist religion, a body of ascetic practices that originated in the Nara Period of Japan having evolved during the 7th century from an amalgamation of beliefs, philosophies, doctrines and ritual systems drawn primarily from Esoteric Buddhism, local folk-religious practices, Shinto, mountain worship, and Taoism. The final purpose of Shugendō is for practitioners to find supernatural power and save themselves and the masses by conducting religious training while treading through steep mountain ranges. Practitioners are called Shugenja (修験者) or Yamabushi (山伏, lit. '"Mountain Prostrator"'). The mountains where Shugendō is practiced are all over Japan, and can span multiple mountains within one range such as the Ōmine mountain range with Mount Hakkyō and Mount Ōmine or the Ishizuchisan mountain range with Kamegamori and Tengudake.

The Shugendō worldview includes a large pantheon of deities (which include Buddhist and Shinto figures). Some of the most important figures are the tantric Buddhist figures of Fudō Myōō and Dainichi Nyorai. Other key figures are Gongen (権現), which are considered to be manifestations of Buddhas sometimes as Japanese kami. Zaō Gongen (蔵王権現) is one of the most important gongen in Shugendō.

Shugendō evolved during the seventh century from an amalgamation of beliefs, philosophies, doctrines and ritual systems drawn from local folk-religious practices, Shinto mountain worship and Buddhism. The seventh-century ascetic and mystic En no Gyōja is widely considered as the patriarch of Shugendō, having first organized Shugendō as a doctrine. Shugendō literally means "the path of training and testing" or "the way to spiritual power through discipline." Some Shugendō practitioners were said to be descendants of the Kōya Hijiri monks of the eighth and ninth centuries.

From the ninth century, elements of Vajrayana Buddhism such as Shingon and Tendai Buddhism were taken into Shugendō and it developed further. In the Heian period, it became very popular among the nobles living in Kyoto to visit Kumano Sanzan (three major shrines, Kumano Hongū Taisha, Kumano Hayatama Taisha and Kumano Nachi Taisha), which was the common holy place of Shugendō, Shinto and Buddhism.

The Meiji government, which erected a barrier between Shinto and Buddhism, ruled that Shugendō was unacceptable because of its amalgamation of the two religions, and officially forbade it in 1872. With the advent of religious freedom in Japan after World War II, Shugendō was revived.

In 1907, Yoshitaro Shibasaki and his team successfully climbed Mount Tsurugi, which was regarded as the last unclimbed mountain in Japan. However, they found a metal cane decoration and a sword on the top of the mountain, and it turned out that someone had reached the top before them. A later scientific investigation revealed that the metal cane decoration and sword dated from the late Nara period to the early Heian period and that shugenja had climbed Mount Tsurugi more than 1,000 years ago.

The Ōmine mountain range, which stretches 100 km from north to south and connects Yoshino and Kumano, was historically the biggest practice place of Shugendō. The highest peak of the Ōmine mountain range is Mount Hakkyō at an altitude of 1915 m, and there are 75 places for ascetic practices along the mountain trail, and Ōminesan-ji Temple at the top of Mount Ōmine at an altitude of 1719 m is considered to be the highest sacred site of Shugendō. At present, the Ōmine mountain range is designated as a UNESCO World Heritage Site "Sacred Sites and Pilgrimage Routes in the Kii Mountain Range" and Yoshino-Kumano National Park.

In modern times, Shugendō is practiced mainly through Shingon and Tendai temples.