Polychlorinated biphenyls (PCBs) are harmful, worldwide chemical pollutants. Most research on the biological effects of PCBs on wildlife has emphasized the lethal effects of PCBs. However, it is well known that PCBs have long lasting reproductive and endocrine effects at sublethal exposures. This thesis investigates the effects of sublethal PCB exposure on bird song, the song system, and song mediated behaviors in both field and captive settings. In the field, black-capped chickadees (Poecile atricapillus) and song sparrows (Melospiza melodia) residing along the PCB-contaminated Hudson River in northeastern New York had higher blood PCB loads compared to individuals from control locations. PCB profiles of the two species varied substantially based on the proportion of lower chlorinated PCBs. High PCB levels correlated with significant, but contrasting effects on bird song structure. High loads were correlated with a greater proportion of black-capped chickadees singing inconsistent songs, and a greater proportion of song sparrows with high performance trills. In captivity, the effects of Aroclor 1242 (the predominant commercial PCB-mixture originally contaminating the Hudson River) and PCB 52, an estrogenic congener, were investigated in zebra finches (Taeniopygia guttata). Results show that young male zebra finches exposed to sublethal PCB dosages learned songs similarly to those of control males, but the treated males reproduce their song with less variability. In addition, PCB-exposure resulted in an increase in dendritic spines in the song motor area HVC, but no changes were seen in the robust nucleus of the arcopallium (RA). Male zebra finches treated with PCBs had altered sexual behaviors, as well as other reproductive parameters, such as increasing the number of nesting attempts before a clutch successfully produces at least one hatchling, increasing the numbers of eggs laid before the first successful clutch, and increasing the number of eggs buried. Female zebra finches treated with Aroclor 1242 had stronger song preferences in a song choice assay. The results of this thesis emphasize that sublethal PCB-exposure during development has subtle but important effects on adult passerine song and behavior, and these effects can have important repercussions to wild populations.