On 30 November 2007, TILEC member Matthijs Nelemans publicly defended his doctoral dissertation entitled 'The prohibition of market manipulation', which was supervised by Prof. M.S. Groenhuijsen and Prof. F.G.H. Kristen. The European prohibition of market manipulation, included in the European Market Abuse Directive, covers both disseminating false or misleading information and trading shares to initiate a price change or to cause an artificial price. Matthijs argues that this prohibition poorly characterizes market manipulation. His dissertation provides an economic background to the relevant issues and offers narrower definitions. One of his conclusions is that the prohibition of information-based manipulation should include a materiality standard in order to exclude minor forms of false or misleading information. Furthermore, the prohibition of trade-based manipulation would benefit from being interpreted in line with his 'unsupported price pressure' standard. Whereas supported price pressure, defined as price pressure that is based on sufficient information, contributes to price efficiency, unsupported price pressure may create social costs.