Residual and cascaded migration can be described as a continuous process of velocity continuation in the post-migration domain. This process moves reflection events on the migrated seismic sections according to changes in the migration velocity. Understanding the laws of velocity continuation is crucially important for a successful application of migration velocity analysis. In this paper, I derive the kinematic laws for the case of prestack residual migration from simple trigonometric principles. The kinematic laws lead to dynamic theory via the method of characteristics. The main theoretical result is a decomposition of prestack velocity continuation into three different components corresponding to residual normal moveout, residual dip moveout, and residual zero-offset migration. The contribution and properties of each of the three components are analyzed separately.