Although the island of Lombok is famed for its strong Islamic bent, to refer to its indigenous Sasak people as religiously orthodox would be sociologically irresponsible at worst, misleading at best. For a great number of Sasaks follow an Islamic tradition known as the Wetu Telu, a highly syncretic religious practice in which Hindu-Javanese, Balinese and elements of indigenous Sasak pre-Islamic culture come together in the local interpretation of Islam. By Jean Couteau

Lombok entered written history when it became a dependency of the empire of Majapahit, which controlled the route to the Spice islands to the East in the 14th and 15th century. A curious historical fact is that it may have been the colonisation of Lombok by the Hindu-Javanese empire that facilitated the entry of Islam to the island. Islamic tombs found on the site of Majapahit suggest that Islam, the religion of most of the traders plying the spice route, was present in the capital of the empire. It is also likely that Moslem traders operated on several coastal areas of the island, as the chronicle of the royal family of Bayan, in the north of the island, talks of people "all abandoning their religion and becoming Moslems" towards the end of the 15th century. Evidence of this early brand of Islam is found in the existence of East Javanese-style mosques in northern Lombok.

Lombok's official conversion to Islam may actually have been a continuation of the Islamisation of Java by the trader-missionaries who destroyed the empire of Majapahit at the beginning of the 16th century, and established sultanate of Demak, known as "the Mecca of the East", which replaced Majapahit for a century. According to two chronicles, the Babad Tanah Jawi and the Babad Lombok - respectively the Java and Lombok chronicles - one of these missionaries, the Lord of Giri (near Surabaya in East Java),having met with success in Java, undertook to send his disciples to the still heathen lands of the East. To the Celebes, Ternate and Tidore he sent Datuk Randan, to Borneo he sent Lembu Mangkurat and to Lombok, Bali and Sumbawa he sent his own son, Sunan Prapen.

Sunan Prapen is said to have arrived in Lombok around 1540. The brand of Islam he taught appears to have been mystical in nature, akin to Islamic Sufism. In this way, he greatly facilitating the incorporation of elements Islam into the existing, pre-Islamic religious practices of which, like Sufism, mysticism was an important part. According to the chronicle, Sunan Prapen trained six disciples, who in turn taught six disciples each, thus spreading the new faith throughout the island. This conversion may not have been a fully religious one, however. Sunan Prapen first converted the king, Prabu Mangkusari, and his disciples were selected among the nobility. As had been the case in Java, the conversion of Lombok's rulers to Islam probably owed more to power allegiances than to religious concerns. Furthermore their conversion was based not on the Arabic Coran itself, but on a Javanese reading of it, thus leaving the text open to polysemic interpretations based on a variety of influences. It was hardly conducive to orthodoxy.

One such influence came from Bali where, by the middle of the 16th century, King Baturenggong's kingdom of Gelgel was at the peak of its power. By securing Blambangan in Java to the West and Lombok and Sumbawa to the East, Baturenggong kept attempts at Islamisation at bay. To this day, the capacity of Gelgel to resist Islamisation is frequently attributed to Baturenggong's priest-minister, Dang Hyang Nirartha, a great reformer of Balinese Hinduism and the builder of many of the island's temples. Before moving to Bali, the priest lived in Kediri (Java), where he is likely to have been in contact with Sufi Moslems. Dang Hyang Nirartha, in whose day Balinese Hindu society was deeply polytheistic, is believed to have been responsible for the dissemination of the monotheistically-inclined Hinduism of modern Bali. It is a tribute to Nirartha's diplomatic skills that the spread of his ideas about a monotheist Hinduism, whilst probably drawing directly on the Islamic emphasis on the Oneness of God, seems to have played an important role in stemming the island's conversion to Islam. This makes Nirartha one of Bali's most key historical figures, for it is probably due to him that Bali has retained the practices which make it, according to historians, like a 'living museum', where a culture reminiscent of that of 14th century Java - at the time when Bali 'annexed' by the Java-based Majapahit - continues to thrive.