The Gaonim were the originators or, at least, the arrangers of parts of the liturgy.
They composed new hymns and invocations, fixed the order of service, and established in full vigor a system of _Minhag_, or Custom, whose power became more and more predominant, not only in religious, but also in social and commercial affairs.
The literary productions of the Gaonic age open with the _Sheeltoth_ written by Achai in the year 760.

This, the first independent book composed after the close of the Talmud, was curiously enough compiled in Palestine, whither Achai had migrated from Persia.

The Sheeltoth ("Inquiries") contain nearly two hundred homilies on the Pentateuch.

In the year 880 another Gaon, Amram by name, prepared a _Siddur_, or Prayer-Book, which includes many remarks on the history of the liturgy and the customs connected with it.

A contemporary of Amram, Zemach, the son of Paltoi, found a different channel for his literary energies.