As you know, when drilling horizontal wells, modern equipment Geo-Pilot, Abto Trak with the inclusion of MWD and LWD systems is used, allowing to monitor the parameters of the deviated well in real time. Availability of this modern equipment certainly allows to carry out successfully the drilling of slanted and horizontal wells. However, the proposed equipment is rather expensive and requires involvement of specialists able to work with these devices. This book deals with the issues of controlling parameters of deviated and horizontal wells, with the help of elastic bottomhole assemblies (BHA). For this purpose, methods of calculation of elastic bottomhole BHA with one and two elastic centralizers as well as BHA with a calibrator and one elastic centralizer (self-oriented) are given. The book also proposes a number of technical devices, such as a removable moving elastic centralizer and a non-orientable hinge arrangement for dialing the zenith angle.