A hallmark of the vast complexity of the brain is the immense number of synapses — the connections between each nerve cell. We have been developing new ‘synaptomics’ tools that can map these billions of synapses and identify their protein components. In the first pioneering step this has revealed unprecedented organisation and diversity in synapse types among the different regions of the mouse brain. To fully understand how these ‘synaptome maps’ contribute to brain development and function, we need to adapt our tools to overcome the challenges presented by the size and complexity of the human brain. We will then generate a synaptome atlas of the whole human brain and also examine key functional areas in detail. This will provide entirely new insight into how the normal human brain works, but also novel tools and resources that can be used to uncover how the synaptome maps go awry in neurological conditions such as schizophrenia, autism and depression. We will link our results in with major international brain research efforts, helping to build a comprehensive picture of brain function of greatest benefit to the maximum number of people, not only in the UK but worldwide.