A Tri-Specific Binding Molecule capable of immunospecifically binding to three different epitopes, comprising: (a) an Antigen-Binding Domain I comprising a VH I Domain and a VL I Domain, capable of immunospecifically binding to an Epitope I present on a first antigen, wherein the Antigen-Binding Domain I is a Diabody-Type Binding Domain; (b) an Antigen-Binding Domain II comprising a VH II Domain and a VL II Domain, capable of immunospecifically binding to an Epitope II present on a second antigen, wherein the Antigen-Binding Domain II is a Diabody-Type Binding Domain; (c) an Antigen-Binding Domain III comprising a VH III Domain and a VL III Domain, capable of immunospecifically binding to an Epitope III present on a third antigen, wherein the Antigen-Binding Domain III is a Non-Diabody-Type Binding Domain; (d) an E-coil Heterodimer-Promoting Domain and a K-coil Heterodimer-Promoting Domain; (e) an Fc Domain that is formed by the association of two CH2-CH3 domains to one another; (f) Cysteine-Containing Domains through which different polypeptide chains are covalently complexed together; (g) a Linker 1 between the VH I Domain and the VL II Domain and between the VH II Domain and the VL I Domain; and (h) a Linker 2 between the VH II Domain and a Heterodimer-Promoting Domain or between the VH I Domain and a Heterodimer-Promoting Domain; wherein: the first antigen, the second antigen and third antigen are the same antigen, or are independently the same or different from another of the antigens; and the Tri-Specific Binding Molecule has the domain structure depicted in any one of Figures 4A, 4C, 4E, 4F, 4H, 4I and 4K; optionally wherein the Tri-Specific Binding Molecule further comprises: (i) a Linker 3 between a Heterodimer-Promoting Domain and one of the CH2-CH3 Domains; (j) a Linker 4 between the VL I Domain and one of the CH2-CH3 domains; (k) a CL Domain; and/or (l) a CH1-Hinge Domain. (a) an Antigen-Binding Domain I comprising a VH I Domain and a VL I Domain, capable of immunospecifically binding to an Epitope I present on a first antigen, wherein the Antigen-Binding Domain I is a Diabody-Type Binding Domain; (b) an Antigen-Binding Domain II comprising a VH II Domain and a VL II Domain, capable of immunospecifically binding to an Epitope II present on a second antigen, wherein the Antigen-Binding Domain II is a Diabody-Type Binding Domain; (c) an Antigen-Binding Domain III comprising a VH III Domain and a VL III Domain, capable of immunospecifically binding to an Epitope III present on a third antigen, wherein the Antigen-Binding Domain III is a Non-Diabody-Type Binding Domain; (d) an E-coil Heterodimer-Promoting Domain and a K-coil Heterodimer-Promoting Domain; (e) an Fc Domain that is formed by the association of two CH2-CH3 domains to one another; (f) Cysteine-Containing Domains through which different polypeptide chains are covalently complexed together; (g) a Linker 1 between the VH I Domain and the VL II Domain and between the VH II Domain and the VL I Domain; and (h) a Linker 2 between the VH II Domain and a Heterodimer-Promoting Domain or between the VH I Domain and a Heterodimer-Promoting Domain; the first antigen, the second antigen and third antigen are the same antigen, or are independently the same or different from another of the antigens; and the Tri-Specific Binding Molecule has the domain structure depicted in any one of Figures 4A, 4C, 4E, 4F, 4H, 4I and 4K; (i) a Linker 3 between a Heterodimer-Promoting Domain and one of the CH2-CH3 Domains; (j) a Linker 4 between the VL I Domain and one of the CH2-CH3 domains; (k) a CL Domain; and/or (l) a CH1-Hinge Domain.