This article reviews photocatalysis for water splitting by various kinds of metal oxides and nitrides such as ferroelectric metal oxides, different kinds of titanates with d⁰ (Ti⁴⁺) electronic configuration as a core metal ion, and various typical metal oxides with d¹⁰ (In³⁺, Ga³⁺, Ge⁴⁺, Sn⁴⁺, Sb⁵⁺) configuration, and d¹⁰ (Ga³⁺) metal nitride, together with d¹⁰s² (Pb²⁺) and d⁰f⁰ (Ce⁴⁺) metal oxides. Ferroelectric metal oxides with single domain structure showed anomalous photovoltaic effects that controlled the behavior of photoexcited electrons. Various metal oxides involving ionic alkaline metal/alkaline earth metal ions showed good correlation between photocatalytic activity and the distortion of octahedral XO₆/tetrahedral XO₄ (X = core metal ion). When the metal oxides involved covalent metal ions such as Zn²⁺ and Pb²⁺, the activity was invoked even in distortion-free structures: this is due to strong electronic effects that affect the band structure. The activity of d¹⁰ metal oxides and nitrides is associated with conduction bands of hybridized sp orbitals with large dispersion that are able to generate photoexcited electrons with large mobility. A feature of the photocatalytically active metal oxides and nitrides discovered so far, which is their closed shell electronic structures is discussed.