This work is the first instalment in the accomplishment of a project entered into more than half a century ago.

In 1930, as a young missionary in South India, I became aware that no coherent and comprehensive account of Christianity in India was available. Protestant writers had dealt cursorily, if at all, with Roman Catholic missions; Roman Catholic writers hardly mentioned Protestant endeavour. Both agreed in regarding the ancient church of the Thomas Christians as a subject for special and separate treatment. Professor K.S. Latourette's great History of the Expansion of Christianity still lay in the future. As that work appeared, with ample bibliographical material in each volume, it inaugurated a new epoch in missionary studies. Yet even Latourette did not feel it in accordance with his purpose to devote space to detailed study of the Thomas Christians.

Hoping that one day I might be able to make some contribution towards filling the gap, I set myself with ardour to the study of the subject. During the next forty years and more, a number of chapters had been written and abandoned in the light of fuller knowledge. Only after retirement from full work in other areas have I been able to make Christianity in India a matter of central concern.

The Christian church has existed in India for at least 1,500 years. It antedates the coming of the first Muslims by two centuries, and the formation of the Sikh religion by a thousand years.