The virtual source method is an geophysical technique to image and monitor the Earth''s subsurface below a complicated and time-varying overburden without the knowledge of overburden velocities and near-surface changes. It is based on extracting the response between a given pair of receivers by correlating the wavefields recorded by them and stacking over the physical sources. The virtual source method requires surface shooting recorded by subsurface receivers placed below the distorting or changing part of the overburden. Redatuming the recorded response to the receiver locations allows the reconstruction of a complete downhole survey as if the sources were also buried at the receiver locations. The ability to redatum the data independent of the knowledge of complicated and time-varying overburden velocities makes the virtual source method a valuable tool for imaging and time-lapse monitoring.