1. What is time-lapse? 2. Various time-lapse methods 3. Active seismic approach by ACROSS (Accurately Controlled and Routinely Operated Signal System) 4. Imaging temporal change by back propagation 5. Passive seismic approach 6. Previous time-lapse other than ACROSS method 7. Case studies based on ACROSS methodology 8. Near-surface effects 9. Repeatability 10. Time-lapse in viewpoint of geomechanics