Dioxin may refer to:

• 1,2-Dioxin or 1,4-Dioxin, two unsaturated heterocyclic 6-membered rings in which two carbon atoms have been replaced by oxygen atoms, which gives the molecular formula C₄H₄O₂
• Dibenzo-1,4-dioxin, also known as dibenzodioxin or dibenzo-p-dioxin (molecular formula C₁₂H₈O₂), in which two benzene rings are connected through two oxygen atoms. That is the parent compound of the dioxins (see next in which the dioxins comprise a key part of the class)
• Dioxins and dioxin-like compounds, a diverse class of chemical compounds that are known to exhibit "dioxin-like" toxicity
• 2,3,7,8-Tetrachlorodibenzodioxin (TCDD), the prototypical example of the above class, often referred to simply as "dioxin"