Gene stacking is the combination of more than one gene for plant disease resistance, or crop productivity, or other horticultural traits.​ In plant breeding traditionally that means breeding those genes in, but increasingly also can mean genetic engineering.​ This can be achieved a few different ways, and gene pyramiding is one of those methods.​ Stacking of transgenes is yet more difficult than stacking natural genes, but especially in the case of pest resistance genes which require a significant financial investment to insert, is advantageous over other methods.