Abstract: Methods and systems for forming a window through the wall of a well casing to enable a new borehole to be drilled outside the casing include forming a cement plug in the casing, drilling a laterally offset hole in the cement plug, orienting and setting a whipstock in the offset hole, and using the whipstock to drill an elongated window through the casing wall opposite its deflector surface. The drilling steps employ a mud motor having a bent housing that establishes a toolface for the bit, and proper orientation is obtained by downhole measurement and transmission to the surface of orientation signals and downhole adjustment of orientation to a selected toolface value. The whipstock is oriented in the same manner. All drilling and orientation procedures are carried out on coiled tubing to reduce costs.