The spread of Islam is one of the most significant processes of Indonesian history, but also one of the most obscure. Muslim traders had apparently been present in some parts of Indonesia for several centuries before Islam
became established within the local communities. When, why and how the conversion of Indonesians began has been debated by several scholars, but no definite conclusions have been possible because the records of Islamisation
that survive are so few, and often so uninformative. In general, two processes probably occurred. On the one hand, indigenous Indonesians came into contact with Islam and made an act of conversion. On the other, foreign Asians (Arabs, Indians, Chinese, and so on) who were already Muslims settled permanently in an Indonesian area, intermarried and adopted local lifestyles to such a degree that in effect they became Javanese or Malay or whatever.
These two processes may often have occurred in conjunction with each other, and when a piece of evidence survives indicating, for instance, that a Muslim dynasty had been established in some area, it is often impossible to know
which of these two processes was the more important.