TCDD may refer to any of the following:
- Turkish State Railways (Türkiye Cumhuriyeti Devlet Demiryolları) - The national railway carrier of Turkey.
- TCDD Taşımacılık - A Turkish transport company responsible for railway operations.
- 2,3,7,8-Tetrachlorodibenzodioxin — a type of dioxin.
- Texas Council for Developmental Disabilities