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The Catalogue of Southern Ringed Galaxies (CSRG) is a comprehensive compilation of angular diameters, axis ratios, relative bar position angles, and morphologies of inner and outer rings, pseudorings, and lenses in 3,692 spiral and S0 galaxies south of declination $-$17$^{\circ}$. The purpose of the catalogue is to evaluate the idea that these ring phenomena are related to orbital resonances with a bar or oval in galaxy potentials. The catalogue, which was begun in 1984, is based on visual inspection of most of the 606 fields of the SRC IIIa-J southern sky survey, with the ESO-B, ESO-R, and Palomar Sky surveys used as auxiliaries when needed for overexposed core regions. Analysis of CSRG data provides some of the strongest evidence yet obtained that observed galaxy rings are linked to specific orbital resonances. Model distributions of apparent axis ratios and bar/ring position angles of thin elliptical rings have been computed which allow for the errors in the observed shapes and angles. These models use Gaussian intrinsic distributions of shapes and angles, and contain the fundamental assumption that the spin axes are randomly oriented to the line of sight. Comparisons with observed distributions indicate that the typical outer feature has an intrinsic axis ratio of 0.87 $\pm$ 0.14 while the typical inner feature has an intrinsic axis ratio of 0.84 $\pm$ 0.10. Weak dependences on family (or apparent bar strength) are found, with SB features being more elongated than SA features. The distributions of bar/ring position angles indicate that outer features have two preferred intrinsic alignment angles with respect to bars: parallel and perpendicular, while inner features have one main preferred intrinsic alignment angle: parallel. These findings strongly link the observed ring features to specific orbital resonances with a bar or oval. Outer features trace the location of the outer Lindblad resonance while inner features trace the location of an ultraharmonic resonance inside corotation. These firm identifications allow the possibility for indirect measurement of the bar pattern speed in many galaxies, and will also provide insight into the secular evolution of galaxy structure.
