Some embodiments include a memory array having a first set of lines extending along a first direction, and a second set of lines over the first set of lines and extending along a second direction. Lines of the second set cross lines of the first set at cross-point locations. Memory structures are within the cross-point locations. Each memory structure includes a top electrode material, a bottom electrode material and a programmable material. Rails of insulative material extend parallel to the lines of the second set and alternate with the lines of the second set along the first direction. The programmable material has first regions within the memory structures and second regions over the rails of insulative material. A planarized surface extends across the lines of the second set and across the second regions of the programmable material. Some embodiments include methods of forming memory arrays.