X-ray　luminescence　is　an　optical　phenomenon　in　which　chemical　compounds　known　as　scintillators　can　emit　short-wavelength　light　upon　the　excitation　of　X-ray　photons.　Since　X-rays　exhibit　well-recognized　advantages　of　deep　penetration　toward　tissues　and　a　minimal　autofluorescence　background　in　biological　samples,　X-ray　luminescence　has　been　increasingly　becoming　a　promising　optical　tool　for　tackling　the　challenges　in　the　fields　of　imaging,　biosensing,　and　theragnostics.　In　recent　years,　the　emergence　of　nanocrystal　scintillators　have　further　expanded　the　application　scenarios　of　X-ray　luminescence,　such　as　high-resolution　X-ray　imaging,　autofluorescence-free　detection　of　biomarkers,　and　noninvasive　phototherapy　in　deep　tissues.　Meanwhile,　X-ray　luminescence　holds　great　promise　in　breaking　the　depth　dependency　of　deep-seated　lesion　treatment　and　achieving　synergistic　radiotherapy　with　phototherapy.　In　this　Account,　we　provide　an　overview　of　recent　advances　in　developing　advanced　X-ray　luminescence　for　applications　in　imaging,　biosensing,　theragnostics,　and　optogenetics　neuromodulation.　We　first　introduce　solution-processed　lead　halide　all-inorganic　perovskite　nanocrystal　scintillators　that　are　able　to　convert　X-ray　photons　to　multicolor　X-ray　luminescence.　We　have　developed　a　perovskite　nanoscintillator-based　X-ray　detector　for　high-resolution　X-ray　imaging　of　the　internal　structure　of　electronic　circuits　and　biological　samples.　We　further　advanced　the　development　of　flexible　X-ray　luminescence　imaging　using　solution-processable　lanthanide-doped　nanoscintillators　featuring　longlived　X-ray　luminescence　to　image　three-dimensional　irregularly　shaped　objects.　We　also　outline　the　general　principles　of　high　contrast　in　vivo　X-ray　luminescence　imaging　which　combines　nanoscintillators　with　functional　biomolecules　such　as　aptamers,　peptides,　and　antibodies.　High-quality　X-ray　luminescence　nanoprobes　were　engineered　to　achieve　the　high-sensitivity　detection　of　various　biomarkers,　which　enabled　the　avoidance　of　interference　from　the　biological　matrix　autofluorescence　and　photon　scattering.　By　marrying　X-ray　luminescence　probes　with　stimuli-responsive　materials,　multifunctional　theragnostic　nanosystems　were　constructed　for　on-demand　synergistic　gas　radiotherapy　with　excellent　therapeutic　effects.　By　taking　advantage　of　the　capability　of　Xrays　to　penetrate　the　skull,　we　also　demonstrated　the　development　of　controllable,　wireless　optogenetic　neuromodulation　using　X-ray　luminescence　probes　while　obviating　damage　from　traditional　optical　fibers.　Furthermore,　we　discussed　in　detail　some　challenges　and　future　development　of　X-ray　luminescence　in　terms　of　scintillator　synthesis　and　surface　modification,　mechanism　studies,　and　their　other　potential　applications　to　provide　useful　guidance　for　further　advancing　the　development　of　X-ray　luminescence.