With more than 30,000 species, fish are the largest and most ancient vertebrate group. Despite their critical roles in many ecosystems and human society, fish genomics lags behind work on birds and mammals. This severely limits our understanding of evolution and hinders progress on the conservation and sustainable use of fish. Here, we announce the Fish10K project, an international collaborative effort aiming to sequence 10,000 representative fish genomes in a systematic manner within ten years, and officially welcome collaborators to join this effort. As a step towards this goal, we herein describe the best practices for the procurement and storage of biospecimens, sequencing, and assembly strategies. To illustrate, we present the genomes of ten fish species from a cohort of 105 species chosen for technology development.