Spermatozoa exhibit remarkable variability in size, shape and performance, and are a key target of sexual selection due to both sperm competition and sperm-female interactions in sexually reproducing taxa. While knowledge of the evolutionary causes and adaptive significance of sperm morphological and behavioral variation is beginning to accumulate, our understanding of the genetic and molecular basis of sperm form and function remains limited. Here, we describe the first avian sperm proteome using LC-MS based discovery proteomics. The Zebra finch is an important model organism for several fields of study, including sperm competition. Thus, knowledge of the protein constituents of sperm may provide new insights into bird sperm biology and provide an important database for taxon-level comparative studies of sperm function. Sperm were isolated and purified from male seminal glomera (the site of sperm storage in passerine birds) and proteins separated by SDS-PAGE and subjected to trypsin digestion. The resulting peptides were analyzed by nano-electrospray mass spectrometry and resulting peptide spectra queried against the T. guttata proteome (uniprot.org) and protein assignments made using Protein Prophet. This approach identified 495 proteins of the zebra finch sperm proteome (ZfSP). Gene Ontology analysis of the major protein classes included numerous categories previously identified in both mammalian and insect sperm proteomes including metabolism/energetics (e.g., oxidoreductases, hydrolases, transferases) and cytoskeletal components of the sperm axoneme and acrosome (e.g., tubulins, dyneins and outer dense fiber proteins). In addition to these known categories, and compared to other defined sperm proteomes, the ZfSP is enriched in actin-related functions and associated processes at, or near, the membrane surface. We view these findings as an important first step in understanding the molecular basis of sperm form and function in a passerine bird, and believe our results will help shed light on the molecular mechanisms underpinning the outcomes of sperm competition and sperm-female interactions.