螺旋是一种像螺线及螺丝的扭纹曲线，为一种在生物学上常见的形状，例如在DNA及多种蛋白质均可发现这种结构。

螺旋分为左旋和右旋。从螺旋中心沿轴线望去，如果螺旋由近至远为逆时针方向，便是左旋，相反则是右旋。大部份螺丝的螺旋是右旋，但在生物结构上左旋和右旋均常见。判断左旋右旋可以用手比对：握拳竖起的大拇指指向轴线方向，假想螺旋是沿着四指方向环绕轴线的，若螺旋延伸的方向和左手大拇指一致则螺旋为左手螺旋，反之为右手螺旋。

两个螺旋交缠在一起称为双股螺旋。

A helix (pl: helixes or helices) is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helices are coil springs and the handrails of spiral staircases. A "filled-in" helix – for example, a spiral ramp – is called a helicoid. Helices are important in biology, as the DNA molecule is formed as two intertwined helices, and many proteins have helical substructures, known as alpha helices. The word helix comes from the Greek word ἕλιξ, "twisted, curved".