Incoherently　illuminated　or　self-luminous　objects　are　composed　of　many　independent　object　points.　Any　two　points　from　the　object　are　spatially　incoherent　whereas　the　two　beams　from　the　same　object　point　are　spatially　coherent.　Incoherent　digital　holography　is　a　technology　of　recording　holograms　of　incoherent　objects　and　reconstructing　three-dimensional　information　of　the　original　object.　The　hologram　of　a　point　object　can　be　formed　based　on　spatial　self-coherence　of　the　beams　by　suitable　optical　beam-splitting　technique　and　the　hologram　of　an　extended　object　is　the　superimposing　of　all　point-holograms　incoherently.　The　investigations　on　incoherent　digital　holography　have　verified　that　this　technique　has　great　potential　in　non-scanning　fluorescent　microscopy,　incoherent　color　holography,　and　incoherent　adaptive　optics.　The　basic　principle　of　incoherent　digital　holography　is　firstly　demonstrated　and　some　typical　incoherent　holographic　imaging　systems　are　summarized.　The　key　imaging　characteristics　and　research　progress　are　analyzed　and　discussed　based　on　self-reference　incoherent　holography.