The eastern oyster Crassostrea virginica is a major aquaculture species for the United States. The Eastern Oyster Breeding Consortium (EOBC) was formed to advance genetics and breeding of the eastern oyster. A core objective of the EOBC is to develop an efficient genotyping platform that can be used for genomic selection as well as genome-wide association studies of complex traits important to oyster aquaculture and biology. In this project, we conducted whole-genome resequencing of 202 eastern oysters for SNP discovery and used the data to develop two high-density SNP arrays, the 566K CvSNP600 and the 66K OysterCv, for the eastern oyster. The sequenced oysters included 179 from Atlantic populations sequenced by EOBC and 23 from the Gulf of Mexico sequenced by the Gulf of Mexico Oyster Genetics and Breeding Research Consortium.