A simple and scalable method to fabricate graphene-cellulose paper (GCP) membranes is reported; these membranes exhibit great advantages as freestanding and binder-free electrodes for fl exible supercapacitors. The GCP electrode consists of a unique three-dimensional interwoven structure of graphene nanosheets and cellulose fi bers and has excellent mechanical fl exibility, good specifi c capacitance and power performance, and excellent cyclic stability. The electrical conductivity of the GCP membrane shows high stability with a decrease of only 6% after being bent 1000 times. This flexible GCP electrode has a high capacitance per geometric area of 81 mF cm ^-2, which is equivalent to a gravimetric capacitance of 120 F g ^-1 of graphene, and retains >99% capacitance over 5000 cycles. Several types of fl exible GCP-based polymer supercapacitors with various architectures are assembled to meet the power-energy requirements of typical fl exible or printable electronics. Under highly fl exible conditions, the supercapacitors show a high capacitance per geometric area of 46 mF cm ^-2 for the complete devices. All the results demonstrate that polymer supercapacitors made using GCP membranes are versatile and may be used for fl exible and portable micropower devices.