Iestyn is a masculine given name, the Welsh equivalent of English Justin, and may refer to:
- Iestyn (saint), Welsh saint of the 6th or 7th centuries
- Iestyn ap Gwrgant (1045–1093), the last ruler of the Welsh kingdom of Morgannwg
- Iestyn Edwards, stage and TV writer/performer, published poet and journalist
- Iestyn Harris (born 1976), Welsh professional rugby league footballer
- Iestyn Thomas (born 1976), Welsh rugby union footballer
- Rhydderch ap Iestyn (died 1033), king of Gwent and Morgannwg in south Wales
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