We now understand the electrical double layer that exists between the minerals that form the rock matrix and the bulk electrolyte which saturates the pores of the rock, at least in the steady state. It is the presence of this double layer that allows the link between the electrical properties and the fluid-flow properties of the rock to exist. In addition, because pore fluid pressure perturbations can be caused by the passage of poroelastic waves, there is also a link between the seismic properties of rocks and their electrical properties. Although postulated more than 70 years ago, there has been an acceleration in the application of electrokinetic and seismoelectric principles to reservoir problems in general and to borehole measurements in particular. In this paper we review briefly the origin of electrokinetic and seismoelectric phenomena before looking at some of the new borehole applications that are being developed.