Sinus Fidei (Latin for "Bay of Faith") is a small basaltic mare feature in the Terra Nivium region of the Moon. It is also located more than 45 km west of the prominent Yangel' crater.
The bay lies northwest of Mare Vaporum which is narrowly linked, a small lies in the middle of that area. Northeast is the rille known as Rima Conon which runs partly in a zig-zag form. Its crater is located north of the bay. Outside the bay, hills dominate the land shore especially to the east, in that location is Conon W, further east is Lacus Felicitatis.