intensity as a function of the magnitude of the scattering vector is the form factor and is the structure factor. When the intensities from low concentrations of particles are extrapolated to infinite dilution, the structure factor is equal to 1 and no longer disturbs the determination of the particle shape from the form factor . One can then easily apply the Guinier approximation (also called Guinier law, after André Guinier), which applies only at the very beginning of the scattering curve, at small q-values. According to the Guinier approximation the intensity at small q depends on the radius of gyration of the particle. An important part of the particle shape determination is usually the distance distribution function , which may be calculated from the intensity using a Fourier transform The distance distribution function is related to the frequency of certain distances within the particle. Therefore, it goes to zero at the largest diameter of the particle. It starts from zero at due to the multiplication by . The shape of the -function already tells something about the shape of the particle. If the function is very symmetric, the particle is also highly symmetric, like a sphere. The distance distribution function should not be confused with the size distribution. The particle shape analysis is especially popular in biological small-angle X-ray scattering, where one determines the shapes of proteins and other natural colloidal polymers. History Small-angle scattering studies were initiated by André Guinier (1937). Subsequently, Peter Debye, Otto Kratky, Günther Porod, R. Hosemann and others developed the theoretical and experimental fundamentals of the method and they were established until around 1960. Later on, new progress in refining the method began in the 1970s and is continuing today. Organisations As a 'low resolution' diffraction technique, the worldwide interests of the small-angle scattering community are promoted and coordinated by the Commission on Small-Angle Scattering of the International Union of Crystallography (IUCr/CSAS). There are also a number of community-led networks and projects. One such network, canSAS - the acronym stands for Collective Action for Nomadic Small-Angle Scatterers, emphasising the global nature of the technique, champions the development of instrumental calibration standards and data file formats. International conferences There is a long history of international conferences on small-angle scattering. These are hosted independently by individual organizations wishing to host the conference. The hosts of the conference are often collaborating with the IUCr/CSAS on the conference details.