The study of NEOs (Near Earth Objects) has considerably been developed in several ways under the huge impulse of the research on the risks of an hazardous collision with the Earth. In this context observations play a very important role. This article attempts to underline their importance in improving our knowledge of these objects and the necessity of organizing dedicated programs. It develops the objectives of these observations, describes methods to perform the detection of new objects, discusses their follow-up and the necessity of finding using archives. It also gives information about the fit of the observations in order to improve the knowledge of the orbits of NEO and about the effect of the planetary theories taken into account in the model. © 2005 Académie des sciences. Published by Elsevier SAS. All rights reserved.