TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper will address some important factors that should be considered when designing drill-strings for horizontal and extended reach wells (ERW). A second paper will look into the issues of casing design for the same type of wells and present some practical field cases and examples of drill-string and casing design for ERW.Buckling of the string and its influence on reach capability, fatigue and directional control will be emphasized.