This chapter considers reductionism, a major aspect of neuroscience research. I consider reductionist claims that we can only understand nervous systems from knowledge of their component parts. I then consider reductionist approaches and what we have learnt by following them, highlighting that a complete reductionist account of any nervous system region hasn’t been and is probably impossible to achieve. I then discuss decomposable hierarchical and non-decomposable heterarchical systems, and how relational aspects suggest we cannot understand the latter systems from cataloguing their individual components. I then discuss two effects that have received little attention despite being known for decades – volume transmission and ephaptic signalling – that highlight the need to consider component parts in relation to the whole system. I finish by discussing non-reductionist views, equipotentiality, cybernetics, the holonomic brain and embodied cognition, highlighting, as many have in the past, that debating between reductionist and non-reductionist approaches is a false dichotomy.