Phosphonate-based scale inhibitors (SIs) have been used in the oil industry for decades. They are excellent inhibitors particularly of Group II sulfate scales and offer several advantages over other classes of oilfield SIs that contain predominantly carboxylate or sulfonate groups. For example, phosphonates show superior binding to reservoir rocks, giving them long squeeze lifetimes. The superior binding means non-polymeric phosphonate molecules can be used, whereas polymers with carboxylate or sulfonate groups need to be polymeric. Phosphonates are also easily detected by atomic absorption spectroscopy. Most phosphonate-based SIs are aminomethylenephosphonates, yet there are many other methods to introduce the phosphonate group into an organic molecule. This review surveys practical routes to synthesize phosphonate-based molecules and investigations that have been carried out for their use as oilfield SIs.