The Treaty of Venice
The Treaty of Venice is a set of accords that most groups in the supernatural world are signatories too. It lays out a set of common rules and understandings that allows members of different groups to get along when they need to. The treaty was signed in Venice in 1584, replacing the older Byzantium accords.
The largest difference between the Treaty of Venice and the Byzantium accords is the strict rules about the revelation of the supernatural world to unaware humans and it's no coincidence that this change was made during the height of the witch trials.
Under the treaty of Venice any member of the signatory organizations may be executed if revealing the existence of the supernatural to a human causes significant harm to any other signatory member. In modern times this accusation is difficult to make stick, and generally requires fairly clear cut examples of someone revealing the supernatural to a human only to have that human turn to a path of vengeance, supernatural hunting or spreading the word indiscriminately. It also doesn't apply if the human goes on to join a signatory group before doing said harm, allowing organizations like the Temple to continue recruiting.
The other main principles of the Treaty are:
Oaths: A member of the supernatural world is considered bound by any oath they make invoking the Treaty of Venice. Anyone who violates this oath owes reparations to the injured party, if they do not pay, their organization will be compelled to on their behalf. While formally this involves stating, I swear by the Treaty of Venice, it is almost always accepted to also simply say, I give you my Venetian word, or I make a Venetian promise.
Treaties: Members of different organizations may at times need to work together, in order to facilitate that the Treaty covers temporary alliances between different members known as Venetian truces. Again the general requirement is to mention the word Venice of Venetian in your proposal of a truce, as well as to stipulate until when it will last either by a date or time or by a particular event. Such as "I offer you a Venetian Truce until sundown." Or "Venetian Truce until we catch this guy?" While under a truce any hostile actions are considered violations. A failure to help your new ally however is not considered a violation.
Hospitality: In order to successfully host meetings and settle disputes, members of different organizations may often need to work together. To extend someone Venetian hospitality covers that individual until they leave the residence or place of business in question. Any harm that befalls them there that you did not do your best to prevent is considered a violation.
Whenever a violation occurs, reparations are determined. The general principle is that the aggrieved is paid back for the offense threefold. If they lost a hundred dollars, they must be paid back three hundred. If they lost a finger, the guilty will lose three fingers. If they were killed, the guilty and two members of his or her family will be put to death.
Such matters are generally resolved by a council involving a representative from each of the two involved organizations and a representative of one other signatory organization, determined by random draw. In most clear cut cases however, the matter does not proceed this far and an organization simple forces their member to par the threefold reparations.