Recent experimental data on inclusive particle yields in hadron-hadron interactions are analyzed from the point of view of their scale-invariant properties. It is shown that the hypothesis of limiting fragmentation does not hold over the entire range of accelerator energies, although it is consistent with the data at the highest energies, where it is satisfied to an accuracy of 3--20\%. The energy dependence of inclusive reactions is in agreement with the predictions of Mueller--Regge phenomenology. Factorization of the leading Regge singularities is confirmed to an accuracy of at least 10\% for many reactions. The observed violation of Feynman's scaling law for the central region of the inclusive spectrum at the highest CERN ISR energies is consistent with the existence of a constant limit as $s\to\infty$ and a certain factorization property. Models which relate hadron-hadron interactions to deep inelastic scattering processes are discussed. An important feature of these considerations is that they allow for the contributions from resonance decays in the stable-particle spectra. The experimental situation regarding the yields of resonances is analyzed in the light of the quark-parton picture.