[en] Between 4400 and 6850 A a total of 39 diffuse absorption features ares described which are certainly or probably of interstellar origin, together with seven more which also may qualify. Equivalent widths of the 17 bands for which the data are most extensive correlate well (approx. = 0.9) with E (B-V), but even better with E (V-I) and other long-wavelength indices which avoid the bend near 4400 A in the interstellar extiction curve. The internal correlation of one line with another is in most cases excellent. Regional effects worsen the general correation with color excess; the most conspicuous discrepancies are in Cyg and Sco-Oph where the band strength per unit color excess is 30 percent lower than elsewhere. Empirical wavelengths established for the narrower diffuse lines make possible comparison with multiple atomic interstellar lines in the same spectra to an accuracy of about 1 km s^-1. The presence of the diffuse lines bears no demonstrated relationship to the type of background star given an adequate amount of extiction: they are seen from type O to at least mig-G and in novae. No support is seen for identification of the minima in Type I supernova spectra with the diffuse interstellar bands. Study of the wavenumbers of the many diffuse lines now known has still not led to identification of the carrier. Arguments are presented that the material is not in the gas, but is a constituent of the very small grains (radius approx. = 300 A) which are believed responsible for the far-ultraviolet extinction. The diffuse-line spectrum can thus properly be considered as fine structure in the interstellar extinction curve