The mechanisms of deoxidation in the electroslag remelting process have been studied, with particular reference to the reactions involving calcium. ESR ingots made with varying deoxidation rates have been examined with respect to their bulk composition and oxide inclusion composition. We find that at high oxygen potentials (% FeO>0.7 in the slag), reactions between slag FeO and the deoxidant predominate. At low oxygen potentials (% FeO<0.2 in the slag) exchange reactions between deoxidant and the slag components control the inclusion composition. At intermediate oxygen potentials, the inclusion composition is strongly influenced by the SiO₂ content of the slag. The manufacture of low-oxygen, low-sulphur steels by ESR will hence require slags with small contents of both SiO₂ and Al₂O₃.