In vivo Magnetic Resonance has revolutionised clinical imaging and given us amazing insights into the large-scale activity and connectivity of the brain. All off this has been achieved by imaging a single molecule, water. In this talk we instead look at how MRI Scanners can be used to image other small metabolites, whether they be neurotransmitters, energy substrates, or markers of cell generation or degradation. We will see how this technology works, what can be imaged, and at what scales and resolutions of imaging. We will then look at how despite being an apparently direct, quantitative, non-invasive measurement technique, validation and interpretation remains a key problem. Finally, we will see how we can make in vivo MR more specific.