This thesis examines the self-assembly of metalloporphyrins on well-defined surfaces. Within this framework, distinct features of surface-confined synthesis are investigated. Characterisation of the surface-confined systems has been performed under ultra-high-vacuum conditions using complementary surface sensitive techniques; namely, scanning tunnelling microscopy, low energy electron diffraction and x-ray photoelectron spectroscopy. The templated self-assembly of (porphyrinato)nickel(II) (NiP) molecules has been investigated on the Ag/Si(111)-(3 × 3)R30º and Ag(111) surfaces. The NiP molecules self-assemble on both the Ag/Si(111)-(3 × 3)R30º and Ag(111) surfaces, growing epitaxially in a manner consistent with coincidence on the former, and point-on-line coincidence on the latter. While no transition from the lattice structure of the first layer is found on the Ag/Si(111)-(3 × 3)R30º surface, the formation of parallel molecular rows aligned along the primitive lattice vectors of the underlying layer is observed on Ag(111). On-surface covalent coupling of (5,10,15,20-tetrabromothien-2-ylporphyrinato)zinc(II) (ZnTBrThP) molecules has been investigated on the Ag(111) and Au(111)-(22  √3) surfaces. When adsorbed on both surfaces, the ZnTBrThP molecules display a latent thermal lability, resulting in the fragmentation of the bromothienyl groups upon annealing. The di- and tetra- (thienyl)porphyrin derivatives are found to predominate on the Ag(111) surface, while the latter is exclusively observed on Au(111)-(22  √3). Subsequent on-surface covalent coupling follows a divergent linkage pattern. Control of the axial coordination of chloro(5,10,15,20-tetraphenylporphyrinato) manganese(III) (Cl-MnTPP) molecules been investigated on the Ag(111) surface. The thermally induced dissociation of the Cl ligand occurs through a heterolytic cleavage of the metal-ligand bond, without the demetallation of the porphyrin complex. Upon exposure of the MnTPP molecules to molecular oxygen, dioxygen axially coordinates to the central Mn atom in a symmetric egde-on geometry, consistent with a peroxo-like oxidation state. The oxygenation of the MnTPP molecules is reversible, with the molecular monolayer behaving as a so-called oxygen carrier.