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Abundance analyses from high-resolution optical spectra are presented for 19Type II Cepheids in the Galactic field. The sample includes both short-period(BL Her) and long-period (W Vir) stars. This is the first extensive abundanceanalysis of these variables. The C, N, and O abundances with similar spreadsfor the BL Her and W Vir show evidence for an atmosphere contaminated with$3\alpha$-process and CN-cycling products. A notable anomaly of the BL Herstars is an overabundance of Na by a factor of about five relative to theirpresumed initial abundances. This overabundance is not seen in the W Vir stars.The abundance anomalies running from mild to extreme in W Vir stars but notseen in the BL Her stars are attributed to dust-gas separation that provides anatmosphere deficient in elements of high condensation temperature, notably Al,Ca, Sc, Ti, and $s$-process elements. Such anomalies have previously been seenamong RV Tau stars which represent a long-period extension of the variabilityenjoyed by the Type II Cepheids. Comments are offered on how the contrastingabundance anomalies of BL Her and W Vir stars may be explained in terms of thestars' evolution from the blue horizontal branch.

The Chemical Compositions of the Type II Cepheids -- The BL Her and W Vir Variables