A nonvolatile memory device includes multiple memory cells including first memory cells and second memory cells. A method of programming the nonvolatile memory device includes: performing first programming to apply a programming forcing voltage to a bit line of each of the first memory cells; and dividing the second memory cells into a first cell group, a second cell group, and a third cell group, based on a threshold voltage of the second memory cells after performing the first programming. The method also includes performing second programming to apply a programming inhibition voltage to the bit line of each of the first memory cells and a bit line of each of memory cells of the first cell group. A level of the programming forcing voltage is lower than that of the programming inhibition voltage.