An ogee ( ) is the name given to objects, elements, and curves—often seen in architecture and building trades—that have been variously described as serpentine-, extended S-,^: 218 or sigmoid-shaped. Ogees consist of a "double curve", the combination of two semicircular curves or arcs that, as a result of a point of inflection from concave to convex or vice versa,^: 218 have ends of the overall curve that point in opposite directions (and have tangents that are approximately parallel).

First seen in textiles in the 12th century, the use of ogee elements—in particular, in the design of arches—has been said to characterise various Gothic and Gothic Revival architectural styles.^: 218 The shape has many such uses in architecture from those periods to the present day, including in the ogee arch in these architectural styles,^: 218 where two ogees oriented as mirror images compose the sides of the arch, and in decorative molding designs, where single ogees are common profiles (see opening image). The term is also used in marine construction. The word was sometimes abbreviated as o-g as early as the 18th century,^: 218 and in millwork trades associated with building construction, ogee is still sometimes written similarly (e.g., as O.G.).