A diagonal is a line segment joining two vertices of a polygon.
Diagonal may also refer to:
![](http://upload.wikimedia.org/wikipedia/commons/thumb/0/0e/2512-%C3%A9chafaudage-R%C3%A9union.jpg/220px-2512-%C3%A9chafaudage-R%C3%A9union.jpg)
- Diagonal brace, a beam used to brace a rectangular structure (such as scaffolding) to withstand strong forces pushing into it
- Diagonal pliers, wire-cutting pliers whose cutting edges intersect the joint rivet "on a diagonal"
- Diagonal lashing, a type of lashing used to bind spars or poles together so that the lashings cross over the poles at an angle
- Diagonal system of control, the method referees and assistant referees use to position themselves in one of the four quadrants of an association football pitch
- Main diagonal, the entries of a matrix whose row and column indices are the same
- Diagonal matrix, a matrix whose entries off the main diagonal are all zero
- Avinguda Diagonal, a street in Barcelona
- Diagonal (newspaper), a Spanish newspaper