Supplies of services present some of the greatest challenges in VAT. They are now rapidly growing in economic performance, and yet they are defined for VAT purposes in a residual way: under the Sixth Directive any transaction that is not a supply of goods is a supply of services. On the one hand this gives supplies of services a deceptively simple definition; on the other hand, it leaves supplies of services at the centre of many of the important difficulties raised by VAT.