Ionotropic alginate hydrogels are versatile materials for a wide range of applications. Their biocompatibility and biodegradability have made them perfect candidates for biomedical applications such as tissue engineering and drug delivery. The vast majority of the research related to ionotropic alginate hydrogels has been conducted on Ca²⁺-cross-linked alginate. However, alginate can produce hydrogels with a large number of divalent and trivalent cations. In recent years, the cross-linking of alginate with Fe³⁺ cations has attracted increasing interest due to its extraordinary properties. The particular coordination of Fe³⁺ cations has been found to be critical for mechanical strength, porosity, swelling and other physicochemical properties of the material rarely seen in other ionotropic alginate hydrogels. In addition, the rich redox chemistry of Fe³⁺ cations has been exploited for a wide range of applications, such as drug delivery, tissue engineering, or environmental remediation. In this review we highlight the state-of-the-art that concerns Fe³⁺-cross-linked alginate hydrogels, encompassing from properties and synthesis to applications and future perspectives. We believe that this review would stimulate innovative ideas and promote the research of this material, leading to novel functional materials with new and emerging applications.