Cissonius (also Cisonius, Cesonius) was an ancient Celtic god. After Visucius, Cissonius was the most common name associated with Mercury.^{[citation needed]}

The name has been interpreted as meaning 'carriage-driver' (from Gaulish cissum 'carriage'), or as 'dream-bringer' (from cit- attached to Gaulish souno- 'sleep, dream').

The forms Cissonius and Cissonia are also attested as personal names.

Cissonius is attested in the province of Germania Superior (Königshofen, Creutzwald, Hohenburg, Cologne, Heddernheim) as well as in Promontogno, Avenches, Saintes, Besançon, where he is frequently associated with the Roman god Mercury. This widespread pattern of veneration suggests that Cissonius was not a local topographical spirit.

In one inscription from Promontogno (Switzerland), Cissonus is identified with Matutinus.

Cissonius alone (without Mercury's name) is also mentioned on the Creuzwald dedication, implying that he may have existed as an independent Celtic deity and not simply as an epithet.