Site response analysis is commonly performed to account for local site effects on ground motion propagation during an earthquake. Most site response analyses focus on the horizontal ground motion, but in reality, the ground is simultaneously subjected to shaking in both the horizontal and vertical directions during an earthquake. The talk will provide an overview of fundamental aspects of vertical site response analysis. A practical methodology allowing the use of existing software will be presented. Finally, the impact of the vertical component of ground motion will be demonstrated in three-dimensional analyses for a KiK-net down-hole array in Japan.