A bailo, also spelled baylo, (singular; baili / bailos is plural) was a diplomat who oversaw the affairs of the Venetians in Constantinople, and was a permanent fixture in Constantinople around 1454.

The traumatic outcomes of Venice’s wars with the sultans made it clear to its rulers that in the Ottoman case the city would have to rely chiefly on diplomatic and political means rather than offensive military efforts to maintain and defend its position in the eastern Mediterranean. The bailo’s job was very extensive because he was both Venice’s political and foreign ambassador. He was very important in maintaining a good relationship between the sultan (Byzantine and later the Ottoman government) and the Venetian government. He was also there to represent and protect Venetian political interests. In Constantinople the bailo worked to solve any misunderstandings between the Ottomans and Venetians. To do this they established contacts and friendships with influential Ottomans and by doing this, they were able to protect their own interests. Unfortunately there were instances where there were difficulties finding replacements. This was often due to not enough qualified replacements, refusal to accept the position and the replacement dying before reaching Constantinople.