| Named By: | Charles Walcott in 1911 |
| Time Period: | Burgess Shale |
| Location: | Canada, British Columbia - Burgess Shale., Possibly also the USA |
| Size: | Largest specimens up to 12.7 centimetres long |
| Diet: | Carnivore |
| Fossil(s): | Well over 100 individuals |
| Classification: | | Arthropoda | Limulavida | |
Sidneyia is an extinct arthropod known from fossils found in the Cambrian-age Burgess Shale formation of British Columbia. 144 specimens of Sidneyia are known from the Greater Phyllopod bed, where they comprise 0.27% of the community.