In this article, the author presents a new methodology to study the concept of accessibility. The approach was created by the "Image et Ville" laboratory in Strasbourg between 1982 and 2002 and led to the development of specific software. Two definitions of accessibility —one theoretical, the other operational —, are given, but the main emphasis of the article is laid on methodology. First, the author explains the basic principles and rules underlying the construction of a database designed for the capture of information on travel times and stay times, for any given means of transport. Next, the different processing procedures, which always associate statistics, modelling and visualisation, are described. Three methods to study system accessibility, based on a global data, are suggested: marginal indices and isopleth or piezopleth maps for potential accessibility, correspondence analysis and point symbol maps with envelopes in order to determine a hierarchy of locations, in terms of accessibility, multidimensional scaling and bidimensional regression in order to "reveal" multipolar functional spaces. Subsystems accessibility studies the accessibility of specific places either through classical procedures such as unipolar isopleth maps or thanks to new methods such as isodistance maps or the construction of unipolar functional spaces. The purpose of this article, illustrated with images of Luxembourg, is purely methodological and no commented geographical examples are given. Nonetheless, this approach (summed up in a general diagram) has been applied to areas ranging from Europe to the city of Strasbourg — giving rise to numerous publications demonstrating its validity on a wide range of scales.