The history of directional drilling may be more than a decade that advances fast in recent years due to the boreholes deeper and deeper in the resource exploration and production. The fundamental knowledge and new development are broadly discussed in order to be better understanding and wise use of the technology. The definition of directional drilling, advances of the technology including borehole planning, borehole survey, measured data processing, telemetry systems, especially for the new development of deviation control like steering drilling tools are demonstrated. The applied fields and borehole types of directional drilling are enumerated. A new concept and technical measures of active control technique in the entire borehole for deep geological directional drilling are proposed.