Attempts at suitable identification of a generally accepted definition of a ‘nanomaterial’ have been going on in Europe and worldwide for some time. Definitions are important from a regulatory perspective as “they assist in establishing the subject matter and scope of what is to be regulated”. However, considering the complexities associated with nanoscience and also the differing opinions on various definitions, this has not been an easy task. Reaching an agreement on fundamental terms and definitions such as ‘nanotechnology’, ‘nanoparticle’, ‘nanoscale’, and a ‘nanomaterial’ is both complex and contested. To date, there is no internationally recognised and accepted definition of a ‘nanomaterial’ even though several definitions have been discussed and proposed by national authorities, scientific committees, international organisations, and other bodies.