Hydrogenase enzymes are nature’s catalysts for hydrogen production and uptake. Understanding how they work may lead to new materials as alternatives for precious metals currently used in H2-utilizing fuel and producer cells. Work described in this thesis focuses on synthetic mimics of the active site of [Fe Fe]-hydrogenases and explores their reactivity towards protons and electrons. Chapter 1 gives a brief overview of the chemistry taking place in hydogenase enzymes with a particular focus on the [Fe Fe]-hydrogenase. The evolution of synthetic models mimicking the structure and function of the enzyme from the late 1990s to the current state of the art is discussed. Chapter 2 describes synthesis of the first {2Fe3S} hydride together with new active site mimics in which bulky substituents are incorporated into the dithiolate bridgehead. A comprehensive examination of their structural features and spectroscopic properties is provided. Chapter 3 reports extensive stopped-flow UV-vis, IR and electrochemical studies for a range of subsite models exploring the relationship between the structure and the reactivity towards protons. It is shown that there is a direct linear free energy relationship between the activation energy for protonation and the energy level of the HOMO. Chapter 4 describes the first characterisation of paramagnetic (mixed-valence) Fe(I)(μ-H)- Fe(II) species which is implicated in metallo-sulfur enzymes as an intermediate in electrocatalytic H2 evolution. An unprecedented super reduced state is detected and characterised using a custom-built spectroelectrochemical cell. Chapter 5 shows how muon spectroscopy may provide a new approach for exploring metallo-hydride chemistry. Future avenues of research in the field of [Fe Fe] chemistry arising from the work described in this thesis are also briefly discussed.