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We present results from an optical study of Compact Steep--Spectrum (CSS) radio galaxies and quasars. The distinguishing characteristic of the CSS class is that their powerful radio lobes do not extend outside the host galaxy. The intrinsically small radio structures are explained either as youthful sources which have not had time to expand into classical doubles or as frustrated sources confined by strong interaction with the interstellar medium.
Using the KPNO $2.1^{\rm m}$ and $4^{\rm m}$ telescopes we have obtained broad band images and both low and high dispersion spectra for a sample of 19 CSS sources. Our data support a picture in which the CSS radio sources are interacting with a considerable amount of gas; although we are unable to distinguish between the normal expansion of a young source and a source which is contained by an exceptionally dense NLR. The most dramatic aspect of the spectra is that as a class, the CSS sources have remarkably broad, structured [OIII]$\lambda5007$ profiles. Such exceptional velocity structure is presumably due to acceleration of the ambient gas by the powerful jets and lobes. We find that CSS sources tend to have luminous, high equivalent width, high excitation line emission, consistent with the presence of a subtantial covering factor in the NLR. Based on the observed line ratios we are unable to find convincing evidence that the radio jet plays a direct role in the ionization.
