[en] The 1990s saw significant non-proliferation related developments in the world, resulting in a new period of safeguards development. Over several years an assessment was made of how to strengthen the effectiveness and improve the efficiency of IAEA safeguards. In May 1997 this culminated in the adoption by the IAEA Board of Governors of a Protocol Additional to Safeguards Agreements which significantly broadens the role of IAEA safeguards. As a consequence, the IAEA safeguards system entered a new era. In 1997 the IAEA began to publish a new series of booklets on safeguards, called the International Nuclear Verification Series (NVS). The objective of these booklets was to help in explaining IAEA safeguards, especially the new developments in safeguards, particularly for facility operators and government officers involved with these topics. The current booklet, which is a revision and update of IAEA/NVS/1, is intended to give a full and balanced description of the techniques and equipment used for both nuclear material accountancy and containment and surveillance measures, and for the new safeguards measure of environmental sampling. A completely new section on data security has been added to describe the specific features that are included in installed equipment systems in order to ensure the authenticity and confidentiality of information. As new verification measures continue to be developed the material in this booklet will be periodically reviewed and updated versions issued. The basic verification measure used by the IAEA is nuclear material accountancy. In applying nuclear material accountancy, IAEA safeguards inspectors make independent measurements to verify quantitatively the amount of nuclear material presented in the State's accounts. For this purpose, inspectors count items (e.g. fuel assemblies, bundles or rods, or containers of powdered compounds of uranium or plutonium) and measure attributes of these items during their inspections using non-destructive analysis (NDA) techniques, and compare their findings with the declared figures and the operator's records. The next level of verification has the aim of detecting whether a fraction of a declared amount is missing (partial defect) and may involve the weighing of items and measurements with NDA techniques such as neutron counting or gamma-ray spectrometry. For detecting bias defects, which would arise if small amounts of material were diverted over a protracted length of time, it is necessary to sample some of the items and to apply physical and chemical analysis techniques having the highest possible accuracy, typically less than one per cent. In order to apply these destructive analysis (DA) techniques, the IAEA requires access to laboratories which use such accurate techniques on a routine basis. Containment and surveillance (C/S) techniques, which are complementary to nuclear material accountancy techniques, are applied in order to maintain continuity of the knowledge gained through IAEA verification, by giving assurance that nuclear material follows predetermined routes, that the integrity of its containment remains unimpaired and that the material is accounted for at the correct measurement points. They also lead to savings in the safeguards inspection effort, e.g. by reducing the frequency of accountancy verification. A variety of C/S techniques are used, primarily optical surveillance and sealing. In remote monitoring, the unattended equipment transmits the data off-site. For unattended and remote monitoring, additional criteria must be met, including high reliability and authentication of the data source. Data communication costs have dropped dramatically in recent years. Data security is an important feature of unattended and remote monitoring systems. Environmental sampling, which allows detection of minute traces of nuclear material, was added to the IAEA's verification measures in the early 1990s as a powerful tool for detecting indications of undeclared nuclear activities. Development of equipment and techniques for safeguards is continuing with the help of national support programmes that assist the IAEA in keeping pace with the evolution of new technology. The IAEA defines the safeguards needs, co-ordinates the support programmes, and tests and evaluates the techniques and the resulting equipment being developed. All aspects of equipment performance are evaluated, including compliance with specifications, reliability and transportability and, most importantly, suitability for use by IAEA inspectors in nuclear facilities. The IAEA has an established quality assurance procedure to authorize equipment and software for routine inspection use. The equipment and techniques highlighted in this booklet are those in frequent use for inspection purposes or in the late stages of development. The overall objective of this publication is to provide a comprehensive overview of the techniques and equipment underlying the implementation of IAEA safeguards