This paper addresses the question "In virtue of what do practical reasons have normative force or justificatory power?" There seems to be good reason to doubt that desires are the source of normativity. However. I argue that the reasons to be suspicious of desire-based accounts of normativity can be overcome by a sufficiently sophisticated account. The position I defend in this paper is one according to which desires, or more generally, pro-attitudes, do constitute values and provide rational justifications of actions when they are organized in the right way.