One of the unshakable predictions of LCDM is that dark matter collapses on larger and larger scales as the universe evolves. As a result, galaxies like are own contain a large number of low mass dark matter subhaloes. Detecting these subhaloes is a key test of LCDM and will allow us to constrain the free-streaming mass of dark matter and hence constrain the properties of the dark matter particle. In this talk I will discuss how stellar tidal streams from disrupting globular clusters are sensitive to dark matter subhaloes and present observations of one stream around the Milky Way which contains signatures consistent with perturbations by dark matter subhaloes in the mass range 10^6-10^7 solar masses. If due to dark matter, this would constrain thermal relic dark matter to have a mass above 9-18 keV. I will discuss alternative, non-dark matter, explanations for these perturbations and end with future prospects for other Milky Way streams.