The Dungeness crab, Cancer magister, is an important resource species, and in Puget Sound, USA, where the adults occur in inshore waters that have summer pH as low as 7.6, future levels are predicted as low as 7.1. Using eggs and larvae from females captured in Puget Sound in late 2012, this laboratory study examined hatching success, larval survival, and larval development rate at target pH of 8.0, 7.5, and 7.1, which represent present open ocean, present coastal upwelling, and projected upwelling conditions. Toward the end of their development, the eggs of one C. magister were exposed to the three treatments and they began to hatch after 22 days. Hatching probability was unaffected by lower pH, but hatching was delayed at pH 7.1. In a second experiment, significantly more C. magister larvae survived after 45 days at pH 8.0 than at the two lower pH: 58, 14, and 21 %. The sizes of the zoeae were unaffected by treatment, but larvae in the low-pH treatments progressed through larval stages more slowly. This study shows that low-pH seawater slows embryonic and early larval development and causes appreciable larval mortality. It suggests that ocean acidification could have a measurable impact on the population dynamics of C. magister.