Copyright law determines who has the right to reproduce, disseminate and modify a large share of the existing creative works, such as literary texts and news reporting, musical works, movies, video games or scientific articles. Copyright thus affects the development of digital markets as well as non-commercial use of creative works. Arguably, empirical research is essential to establish how the copyright system affects various stakeholders, and thus to develop adequate policy. This chapter reports on the empirical research regarding the socio-economic consequences of unauthorized copying and copyright. Much empirical work has addressed the effects of unauthorized, digital copying on demand for authorized copies, in particular in markets for musical recordings and movies. That is a central question for assessing how copying affects rights holders, but it is not sufficient to inform copyright policy, because usersí interests also have to be taken into account. Accordingly, this chapter reports on empirical evidence on: (1) the effect of variations in copyright protection on the supply of creative works, which is important in determining how users are affected; (2) administration and transaction costs of copyright systems; (3) unintended effects of copyright regarding competition and technological innovation; and (4) basic findings on the determinants of unauthorized copying. Furthermore, the chapter discusses how these topics relate to one another in terms of a social welfare analysis, including the interests of all stakeholders. This is essential in moving from empirical results to an informed discussion on copyright policy.