This article wants to look at the problem of the relation between Islam and Christianity and their definitions of civilization or religion, from the angles of the Indonesian Muslims and Christians. In the colonial past both Islam and Christianity behaved like complete communities or civilizations. Therefore religious affiliation had always social and political impact and it was and is often not possible to change religion, like people cannot change their ethnic or gender status. During the pastfifty years there has been a tendency towards a pluralist society, not taking religious identity as a major classification mark. The uncertainties after the fall of President Soeharto (May 1998) and the aftermath of increasing Muslim-Christian conflicts, challenge this development.