Ferromagnetic　transition　has　generally　been　considered　to　involve　only　an　ordering　of　magnetic　moment　with　no　change　in　the　host　crystal　structure　or　symmetry,　as　evidenced　by　a　wealth　of　crystal　structure　data　from　conventional　X-ray　diffractometry　(XRD).　However,　the　existence　of　magnetostriction　in　all　known　ferromagnetic　systems　indicates　that　the　magnetic　moment　is　coupled　to　the　crystal　lattice;　hence　there　is　a　possibility　that　magnetic　ordering　may　cause　a　change　in　crystal　structure.　With　the　development　of　high-resolution　synchrotron　XRD,　more　and　more　magnetic　transitions　have　been　found　to　be　accompanied　by　simultaneous　structural　changes.　In　this　article,　we　review　our　recent　progress　in　understanding　the　structural　change　at　a　ferromagnetic　transition,　including　synchrotron　XRD　evidence　of　structural　changes　at　the　ferromagnetic　transition,　a　phenomenological　theory　of　crystal　structure　changes　accompanying　ferromagnetic　transitions,　new　insight　into　magnetic　morphotropic　phase　boundaries　(MPB)　and　so　on.　Two　intriguing　implications　of　non-centric　symmetry　in　the　ferromagnetic　phase　and　the　first-order　nature　of　ferromagnetic　transition　are　also　discussed　here.　In　short,　this　review　is　intended　to　give　a　self-consistent　and　logical　account　of　structural　change　occurring　simultaneously　with　a　ferromagnetic　transition,　which　may　provide　new　insight　for　developing　highly　magneto-responsive　materials.