The epi tōn deēseōn (Greek: ὁ ἐπὶ τῶν δεήσεων, "the one in charge of petitions") was a Byzantine office, whose holder was responsible for receiving and answering petitions to the Byzantine emperor. Subordinate officials with the same title also existed in the provinces, and the Patriarch of Constantinople also had an epi tōn deēseōn.
The office is usually considered (cf. Bury) as the direct continuation of the late Roman magister memoriae, but this identification is not certain. The title is first attested in a 7th-century seal. In the lists of precedence like the Klētorologion, he was counted among the judicial officials (kritai), and surviving seals show that until the 11th century, its holders held relatively mid-ranking dignities, no higher than prōtospatharios. From the latter half of the 11th century however and during the 12th, the office rose much in importance, with its holders receiving higher titles and being drawn from among the Empire's nobility. The last named holder, George Chatzikes, is attested in 1321, but the office is still mentioned as active decades later by Pseudo-Kodinos.
It is unknown if he had a dedicated staff (officium), or what its composition may have been; it is absent in the Klētorologion, but a seal of a probably subordinate "notary of the petitions" (notarios tōn deēseōn) is known. Seals also attest to the existence of provincial officials titled epi tōn deēseōn, as in Sicily and the Peloponnese.