| Gridreference: | NF880913 |
| Coordinates: | 57.8°N -7.25°W |
| Location Map: | Scotland Outer Hebrides |
| Caption: | Shillay shown within the Outer Hebrides |
| Celtic Name: | Siolaigh |
| Norse Name: | selr-øy |
| Meaning Of Name: | seal island |
| Area: | 47 ha (116 acres) |
| Area Rank: | 208 |
| Highest Elevation: | 79 m (259 ft) |
| Population: | 0 |
| Island Group: | Lewis and Harris |
| Local Authority: | Na h-Eileanan Siar |
Shillay (Gaelic; Scottish Gaelic: Siolaigh) is an uninhabited island which lies 2 km north of Pabbay in the Outer Hebrides of Scotland.
The name is derived from the Norse selr-øy meaning seal island and is a Scottish Wildlife Trust reserve owing to its international importance for breeding grey seals.
There is no record or evidence that it has ever seen human habitation.