Buddhism was a world religion that had existed for 1,000 years when emissaries from the king of the more advanced Korean state of Paekche introduced this complex array of beliefs to the Japanese in 552 CE. Buddha, meaning ''enlightened one,'' was born Prince Gautama Siddhartha in the Indian Shakya nation around 563 BCE and died in 483. Siddhartha was a human and only later deified. According to the story of the founding of Buddhism, written centuries after Siddhartha's death, the young boy was brought up in luxury and protected from the evils of the world by his parents. However, Siddhartha ventured from the safe confines of the palace and encountered old age, sickness, and death. Siddhartha was extremely troubled by these ultimate realities of human existence and, abandoning his privileged life and his family, pursued the life of the wandering religious seeker.

For a number of years Siddhartha engaged in such practices as extensive fasting that almost killed him. Finally, he settled on a middle way that preserved his life but did not lead to overindulgence in the world's pleasures. After extensive meditation under the bodhi, or ''wisdom tree,'' Siddhartha became enlightened and spent the rest of his life bringing his teachings to a growing number of disciples. From Siddhartha's evolution to Buddha, a world religion was born.

The Four Noble Truths constitute the essence of Buddhist teachings, though they are now greatly augmented by an entire canon of theological literature. The first Truth is that life is suffering. To be human is to suffer, and such tribulations as pain and old age are impossible to avoid. Integrated with this teaching are the notions of karma, reincarnation, and nirvana. The principle of karma focuses on human action and moral results. Both good and evil deeds accrue for the individual. If an individual lives a good life, he or she will be born again, or reincarnated, in a better life. Still, all human life means suffering, so the ultimate spiritual goal is not to continue to be born or reincarnated again but rather to achieve nirvana, where one transcends the repeating life cycle and is never reborn.

The second and third Truths expand on the first Truth. In the second Truth, desire is clearly identified as the cause of human suffering. The third Truth is an injunction that if humans want to stop suffering they must extinguish desire. This goal is achieved through such religious practices as meditation and through following the fourth Truth, or the Eightfold Path, which includes right views, right intention, right speech, right action, right livelihood, right effort, right mindfulness, and right concentration.

As Buddhism matured in India, its theology became more complex, and other concepts became important to the belief system as well. One major Buddhist tenet critical to understanding the religion is that the notion that each individual possesses a ''soul'' is incorrect. Because to live is to change, any individual is a compilation of his or her attributes at any given point in time. Human attributes are not permanent and change as time passes. Buddhism also divided into two major schools relatively early in its history: Theravada, which is today dominant in most of Southeast Asia, and Mahayana, which spread to China, Korea, and then Japan and is still the general institutional framework for the many Buddhist denominations in existence in Northeast Asia today.

Although Mahayana and Theravada Buddhists agree on key points, there are also significant differences on some basic beliefs. While the ultimate goal of Theravada Buddhism is individual enlightenment, Mahayana Buddhists embrace the concept of Bodhisattvas, or ''enlightened ones,'' who delay their own accession into nirvana in order to help other sentient beings realize this state. Also, Mahayana Buddhism encouraged the growth of devotion toward not only the Buddha but a pantheon of other Buddhas including Kannon, the Buddha of Mercy; Maitreya, the Buddha of the Future; and Amida, the Buddha of Infinite Light. One eventual effect of Mahayana Buddhism was to make the religion popular among common people who, lacking the education to understand complex philosophical points, could embrace specific sects that deified certain Buddhas such as Amida.

When Buddhism first reached Japan from the Korean Peninsula—along with other vestiges of traditional Chinese culture including written language, art, much of it religious in nature, and philosophical tracts—the Japanese who encountered the foreign religion considered it a form of powerful magic similar to kami. Later during the Heian period, the aristocracy began to embrace such elements of the spiritual messages of Buddhism as the intransience of life and the ideal of giving up attachments. Several sects became popular then including, most notably, Shingon, an esoteric Buddhism introduced by Kukai, who had traveled to China to study the sect. Shingon, which remains the third largest of the Japanese Buddhist sects today, includes intricate and symbolic modes of meditation, mandalas, and distinctive art forms.

By the late Heian era and particularly during the Kamakura period that followed, another Chinese import, Pure Land Buddhism, became the first sect that appealed to the masses. Today, the Pure Land and True Pure Land sects claim the largest number of adherents in Japan. In Pure Land Buddhism, salvation can be gained by praying to Amida, the Buddha of the Western Paradise, and when salvation is gained one can be reborn in this paradise.

Although the sect had arrived earlier, it was during the Kamakura years and the Ashikaga period that followed that Japanese elites including the samurai embraced yet another Chinese import, Ch'an, or in Japanese, Zen Buddhism. Zen would have more profound effects on the culture of the archipelago than was the case in either China or the Korean Peninsula. Today, Zen temples and adherents rank second to the Pure Land sects in Japan, and without a doubt Zen is Japan's most famous world spiritual export. The meaning of Zen is ''quietude'' or ''meditation,'' and Bodhidharma, the Indian monk who came to China and spread its teachings, perhaps best defined the sect in the following lines that are attributed to him:

A special transmission outside the scriptures,
Not founded upon words and letters;
By pointing directly to [one's] mind
It lets one see into [one's own true] nature and [thus] attain Buddhahood.
(Dumoulin 2005, 85)

This form of Buddhism was in important ways originally a Chinese adaptation of Daoist beliefs to imported Buddhism. Japanese Zen was also influenced by Shinto's focus on nature. Although there are differences between Rinzai and Soto, Japan's two largest Zen schools, adherents of both perspectives agree on the beliefs that enlightenment is obtained not through deep reading, study, or philosophical reflection but through zazen, or meditation. Dogen (1200–1253), who was and remains the most revered Zen master in Japan's history, emphasized intense meditation and refused to compromise with the more worldly Buddhist figures of authority in Kyoto. Dogen abandoned Kyoto and moved to a more remote area of Japan. Zen, with its emphasis on austerity, nature, the understated, and the subtle, has been responsible for influencing some of the most famous aspects of traditional Japanese culture. Zen profoundly influenced such martial arts as karate, judo, and kendo (''the way of the sword'') as well as haiku, ikebana, calligraphy, and the construction of Japanese gardens.

Thanks initially to the efforts of Suzuki Daisetsu (1870–1952), an academic, a prolific writer who was published in Japanese and English, and a master popularizer, a few accessible books about Zen were available in North America and the United States by the 1930s. Shortly after World War II and particularly in the 1950s and 1960s with the rise of the ''beat'' poets in the United States, such high-profile writers as Allen Ginsberg, Jack Kerouac, and Gary Snyder and the English writer Alan Watts introduced millions in the West to basic ideas of Zen. Today, Buddhism and in particular Zen (followed by Tibetan Buddhism) has adherents throughout Europe and the United States. Nishida Kitaro (1870–1945), Japan's most famous philosopher and a lifelong friend of Suzuki, integrated the Western philosophical ideas of Henri Bergson and William James with elements of Zen.

Eventual translations of Nishida's work created opportunities for academics throughout the world to consider Zen-based intellectual discourse. Even though Zen Buddhism did not originate on the Japanese archipelago, its ideas have global impact because of individual Japanese who lucidly and beautifully articulated its spiritual practices and, just as important, Zen cultural aesthetics.

The post–World War II globalization of Zen ironically resulted in a rediscovery of the sect in Japan, particularly by some young people who became interested because of their awareness that it had attracted the attention of Westerners. Also, in the years since World War II, some Zen temples have formed associations with private companies who've sent recruits to be trained in hard meditation as a form of ''boot camp'' to inspire selflessness, concentration, and group loyalty. Both developments are partially indicative that Western popularity notwithstanding, within postwar Japan the situation has not been favorable for Zen or other forms of traditional Buddhism. Although there are devout Buddhists and Zen meditation adherents, today most Japanese limit their relationship with Buddhism to using priests for funerals and visiting culturally or historically important temples. The fact that many of the younger generations were ignorant of their own Buddhist traditions until foreigners stimulated their interest is indicative of the decline of regular temple affiliation and spiritual observances on the part of most Buddhist parishioners.

During the early modern period, the Tokugawa government (1600–1868), in an effort to discover hidden Christians, forced every Japanese family to register with a Buddhist temple. Since the majority of Japanese lived in the countryside and small villages and towns until 1945, concrete relations existed between ordinary people throughout Japan and Buddhist temples and priests. However, with the great rural to urban demographic shift of the 20th century, many Japanese families lost connections with their family temples and now use whatever temple is available in the cities only for funerals or on other rare occasions. While Buddhism's influence on daily practice and individual belief systems seems to have diminished in contemporary Japan, beliefs attributed to the teachings of the Chinese sage Confucius, while challenged by the forces of modernity, apparently remain deeply rooted among many Japanese.