The Galaxy Z Fold4 5G is a book style phone with a 6.9 cover display and a 7.6" large main display when unfolded and the Galaxy Z Flip4 is a flip phone style with compact design that unfolds to a 6.5" screen. Also the Galaxy Z Fold4 has three rear cameras while the Galaxy Z Flip4 has two. Only the Galaxy Z Fold4 is S Pen compatible (sold separately).