GNOM is an indirect transform program for small-angle scattering data processing. It reads in one-dimensional scattering curves (possibly smeared with instrumental distortions) and evaluates the particle distance distribution function P(r) (for monodisperse systems) or the size distribution function D(R) (for polydisperse systems). The main equations relating the scattering intensity to the distribution functions and describing the smearing effects one can find in the text-books (e.g. [1]). GNOM is similar to the known programs of Glatter [2], Moore [3] and Provencher [4]. There are, however, some points, which make GNOM more convenient in application. GNOM is a dialogue program; the user instructions presented here explain how to answer the questions properly. The versions E4.0 and higher make use of the "configuration file", where some or all the parameters can be pre-defined; this allows to work with GNOM in different modes, ranging from fully interactive to batch mode. The names of the parameters in the following description refer to the configuration file names. The algorithms used in the program are described elsewhere [4-6]. They are based on the Tikhonov's regularization technique [8]; several subroutines published in [9] are modified and used in GNOM. The value of the regularization parameter is estimated by the program automatically using the perceptual criteria [10].