The　growing　demands　for　X-ray　imaging　applications　impose　diverse　and　stringent　requirements　on　advanced　X-ray　detectors.　Among　these,　flexibility　stands　out　as　the　most　expected　characteristic　for　next-generation　X-ray　detectors.　Flexible　X-ray　detectors　can　spatially　conform　to　nonflat　surfaces,　substantially　improving　the　imaging　resolution,　reducing　the　X-ray　exposure　dosage,　and　enabling　extended　application　opportunities　that　are　hardly　achievable　by　conventional　rigid　flat-panel　detectors.　Over　the　past　years,　indirect-　and　direct-conversion　flexible　X-ray　detectors　have　made　marvelous　achievements.　In　particular,　microscale　and　nanoscale　engineering　technologies　play　a　pivotal　role　in　defining　the　optical,　electrical,　and　mechanical　properties　of　flexible　X-ray　detectors.　In　this　Perspective,　we　spotlight　recent　landmark　advancements　in　flexible　X-ray　detectors　from　the　aspects　of　micro/nano　engineering　strategies,　which　are　broadly　categorized　into　two　prevailing　modalities:　materials-in-substrate　and　materials-on-substrate.　We　also　discuss　existing　challenges　hindering　the　development　of　flexible　X-ray　detectors,　as　well　as　prospective　research　opportunities　to　mitigate　these　issues.