thumb|[[Gautama Buddha in Greco-Buddhist style, 1st–2nd century AD, Gandhara (Peshawar basin, modern day Pakistan).]]

thumb|upright=1.5|[[Silk Road transmission of Buddhism|Buddhist expansion in Asia: Mahayana Buddhism first entered the Chinese Empire (Han dynasty) through Silk Road during the Kushan Era. The overland and maritime "Silk Roads" were interlinked and complementary, forming what scholars have called the "great circle of Buddhism".]]

Greco-Buddhism or Graeco-Buddhism was Buddhism within the Hellenistic period of South and Central Asia, resulting in Greek cultural syncretism developing between the 4th century BC and the 5th century AD in Gandhara, which is located in present-day Pakistan and parts of north-east Afghanistan. While the Greco-Buddhist art shows clear Hellenistic influences, the majority of scholars do not assume a noticeable Greek influence on Gandharan Buddhism beyond the artistic realm.]]

The introduction of Hellenistic Greece to central Asia started after the conquest of that region by Darius the Great and his Persian Achaemenid Empire. He and his successors also conquered the Anatolian peninsula, which at the time was inhabited by many Greek cultures. When they rebelled, those Greeks were often ethnically cleansed by being relocated to the far end of the Persian Empire, those central Asian provinces. When Alexander the Great conquered Achaemenid Empire and further regions of Central Asia in 334 BC, he thus encountered many Greeks already established in the easternmost stretches of its empire. He then ventured into Punjab (land of five rivers). Alexander crossed the Indus and Jhelum River when defeating Porus and appointing him as a satrap following the Battle of the Hydaspes. Alexander's army would mutiny and retreat along the Beas River when confronted by the Nanda Empire, thus would not conquer Punjab entirely.

Thanks to relocation by the Persian Empire, there was established Greek culture in the far east of Alexander's empire. He founded several cities in his new territories in the areas of the Amu Darya and Bactria, and Greek settlements further extended to the Khyber Pass, Gandhara (see Taxila), and the Punjab. Following Alexander's death on 10 June 323 BC, the Diadochi or "successors" founded their own kingdoms. General Seleucus set up the Seleucid Empire in Anatolia and Central Asia and extended as far as India.

The Mauryan Empire, founded by Chandragupta Maurya, would first conquer the Nanda Empire. Chandragupta would then defeat the Seleucid Empire during the Seleucid-Mauryan War. This resulted in the transfer of the Macedonian satraps in the Indus Valley and Gandhara to the Mauryan Empire. Furthermore, a marriage alliance was enacted which granted Seleucus's daughter as Chandragupta's wife for diplomatic relations. The conflict additionally led to the transfer of 500 war elephants to the Seleucid Empire from the Mauryan Empire, presumably as reparations for lives lost and damages sustained.

The Mauryan Emperor Ashoka established the largest Indian empire. Following the destructive Kalinga War, Ashoka converted to Buddhism. Abandoning an expansionist agenda, Ashoka would adopt humanitarian reformation in place. As ascribed in the Edicts of Ashoka, the Emperor spread Dharma, interpreted as Buddhism throughout his empire. Ashoka claims to have converted many, including the Greek populations within his realm to Buddhism:

The decline and overthrow of the Mauryans by the Shunga Empire, and of the revolt of Bactria in the Seleucid Empire led to the formation of the Greco-Bactrian Kingdom (250–125 BC). To their north, the Greco-Bactrians were followed by the secession of the Indo-Greek Kingdom (180 BC – 10 AD). Even when, centuries later, these Hellenized regions were conquered first by the Yuezhi, then by the Indo-Scythians and the Kushan Empire (1st–3rd centuries AD), Buddhism continued to thrive there.

Buddhism in India was a major religion for centuries until a major Hindu revival from around the 5th century, with remaining strongholds such as Bengal largely ended during the Islamic invasions of India.

Cultural interaction

The length of the Greek presence in Central Asia and northern India provided opportunities for interaction, not only on the artistic but also on the religious plane.

Alexander the Great in Bactria and India (331–325 BC)

thumb|upright|"Victory coin" of [[Alexander the Great, minted in Babylon 322 BC, following his campaigns in ancient India.<br/>Obverse: Alexander being crowned by Nike.<br/>Reverse: Alexander attacking King Porus on his elephant.<br/>Silver. British Museum.]]

When Alexander invaded Bactria and Gandhara, these areas may already have been under Sramanic influence, likely Buddhist and Jain. According to a legend preserved in the Pali Canon, two merchant brothers from Kamsabhoga in Bactria, Tapassu and Bhallika, visited Gautama Buddha and became his disciples. The legend states that they then returned home and spread the Buddha's teaching. In 326 BC, Alexander conquered the Northern region of India. King Ambhi of Taxila, known as Taxiles, surrendered his city, a notable Buddhist center, to Alexander. Alexander fought a battle against King Porus of Pauravas in Punjab, the Battle of the Hydaspes in 326 BC.

Mauryan Empire (322–183 BC)

The Mauryan Empire would later defeat the successor Seleucid Empire, during the Seleucid-Mauryan War. Resulting in the transfer of the satraps in the Indus Valley and Gandhara, that had been part of the Achaemenid, Macedonian and Seleucidian, to the Mauryan Empire. However, contacts were kept with his Greco-Iranian neighbors in the Seleucid Empire. Emperor Seleucus I Nicator came to a marital agreement as part of a peace treaty, and several Greeks, such as the historian Megasthenes, resided at the Mauryan court.

thumb|upright|The [[Hellenistic Pataliputra capital, discovered in Pataliputra, capital of the Maurya Empire, dated to the 3rd century BC.]]

Chandragupta's grandson Ashoka embraced the Buddhist faith and became a great proselytizer in the line of the traditional Pali canon of Theravada Buddhism, insisting on non-violence to humans and animals (ahimsa), and general precepts regulating the life of laypeople.

According to the Edicts of Ashoka, set in stone, some of them written in Greek and some in Aramaic, the official language of the Achaemenids, he sent Buddhist emissaries to the Greek lands in Asia and as far as the Mediterranean. The edicts name each of the rulers of the Hellenistic period:

Ashoka also claims he converted to Buddhism Greek populations within his realm: