Some embodiments include a memory array having a first series of access/sense lines which extend along a first direction, a second series of access/sense lines over the first series of access/sense lines and which extend along a second direction substantially orthogonal to the first direction, and memory cells vertically between the first and second series of access/sense lines. Each memory cell is uniquely addressed by a combination of an access/sense line from the first series and an access/sense line from the second series. The memory cells have programmable material. At least some of the programmable material within each memory cell is a polygonal structure having a sidewall that extends along a third direction which is different from the first and second directions. Some embodiments include methods of forming memory arrays.