Part I : Why did people follow Jesus? -- Focussing the question -- Some answers to the question -- Rethinking the evidence -- Charismatic leaders of new religious movements -- The followers of such leaders -- Summing up: the attraction of Jesus -- Part II : Why did Gentiles become Christians? -- Preliminary remarks -- A brief history of the recent discussion of the issue -- Conversion to new religious movements in recent times -- The early Christian evidence -- Christianity's competitors -- Social-scientific evaluation of the evidence -- Summary -- Part III : Why did Christianity succeed in the Roman Empire? -- The problem -- A.D. Nock's proposals -- Rodney Stark's proposals -- Further possibilities -- Summary.