OMiCC is a community-based, biologist-friendly web platform for creating and (meta-) analyzing annotated gene-expression data compendia across studies and technology platforms for more than 24,000 human and mouse studies from Gene Expression Omnibus (GEO). An important feature of OMiCC is that it allows users to contribute to the community by sharing meta-data essential for data collation, reuse, and (meta-) analysis across studies. Thus, users of OMiCC can reuse sample groupings and pairings created by other users to construct cross-study data sets. We envision that as more users take advantage of OMiCC to perform biological hypothesis generation and discovery, more users will create and share such meta-data as well as data compendia and analyses with the biomedical research community.