San Francisco Bay and its estuary is a heavily invaded region due to organisms arriving in ballast water and on fouled ships, as well as with the intentional release of non-native species. Recent crab invasions rendered previous means to identify crab larvae unusable. We provide an illustrated dichotomous key with descriptions of stage I zoeae, and to facilitate identification use external characters that remain definitive through all zoeal stages. Crab zoeae included in this key are as follows: Cancer antennarius, Cancer gracilis, Cancer magister, Cancer productus, Carcinus maenas, Eriocheir sinensis, Hemigrapsus nudus, Hemigrapsus oregonensis, Lophopanopeus bellus, Rhithropanopeus harrisii, Pachygrapsus crassipes, Pyromaia tuberculata, and the family Pinnotheridae. This work aims to provide a tool to aid in the understanding of brachyuran zoeae of the San Francisco Bay and estuary.