The purpose of this paper is to critically analyse research about inclusive education. Prior reviews and the outcome of a recent search of databases are analysed with regard to (a) how inclusion is defined and (b) what empirical knowledge there is regarding factors that make schools and classrooms more inclusive. Our point of departure is that we regard inclusion as an idea about what school systems, schools and classrooms should accomplish, and as such, an expression of an educational philosophy. Four different understandings of inclusive education were found: (a) inclusion as the placement of pupils with disabilities in mainstream classrooms, (b) inclusion as meeting the social/academic needs of pupils with disabilities, (c) inclusion as meeting the social/academic needs of all pupils and (d) inclusion as creation of communities. Under a strict definition of inclusive education, hardly any research was found which reliably identified factors that give rise to inclusive processes. The outcome of our analyses are discussed from the perspective that different understandings of inclusion should be seen, to a large extent, as expressions of different views of what schools should accomplish. We also propose that some of the adherents to inclusion as creation of communities can be placed in the grand educational tradition reaching back to Dewey that tries to establish new ideals for school systems in a society in which individualism is perhaps the main ideology. The main conclusions are that the operative meaning of inclusion in reviews and empirical research should be much more clearly defined and that new types of studies are needed.