Nucleonic gauges or nucleonic control systems (NCSs) have been widely used in the industries of both developed and developing Member States to increase the recovery of oil and minerals, to improve the quality of the products derived from them and to optimize industrial processing of raw materials. It is considered that of all industrial radioisotope techniques, NCS technology is by far the most requested among other industrial radioisotope techniques. Their economic benefits have been widely demonstrated and recognized by industry. There are several hundred thousand nucleonic gauges serving industries worldwide. This nucleonic gauge manual and directory provides a reference database of nucleonic control systems available to potential users in the fields of exploration, exploitation and processing of natural resources and manufacturing industries. The basic principles of the most popular techniques are reviewed and reference data links to suppliers are provided. Information sheets on many typical commercial devices are also included. It will help end users to select the most suitable alternative to solve a particular problem or to measure a certain parameter in a specific process.