The "Oaths of Dagon" were the three principles on which the Esoteric Order of Dagon was based and on which the citizens of Innsmouth lived (or were forced to). There was also "The Proviso to all Oaths", which is to be taken before them.
During 1846, after Obed Marsh was imprisoned by a crowd of people, the Deep Ones attack Innsmouth en masse, killing half of the population and forcing the other to swore the Oaths to Dagon. Interestingly, one is not forced to take all of them, as some refused to swear the third oath, like Old Zadok. But they would be heavily shunned by Innsmouth's new rulers.
The Oaths went like this:
- THE PROVISO TO ALL OATHS: I'a! Dagon! I submit to the authority of the Esoteric Order of Dagon. If I should betray these sacred Oaths, I am theirs to try, and to punish, according to the ancient laws and the extend of my transgression. I'a! Dagon!
- THE FIRST OATH: I'a! Dagon! I swear that I shall keep faith with the Deep Ones in all things. I shall not resist their will, nor shall I betray their secrets.
- THE SECOND OATH: I'a! Dagon! I swear that I shall serve the Deep Ones in all things, as they shall command me, to the furthest extend of my ability.
- THE THIRD OATH: I'a! Dagon! I'a! Hydra! I take this child of Dagon and Hydra as my (wife or husband), to take into my home, to beget and raise children; so that the race, and the faith, shall continue to prosper.