Partial phases
Look at the Sun only through eclipse glasses that comply with ISO 12312-2 or through a correctly fitted front-mounted solar filter. Ordinary sunglasses are not safe.
Optical equipment
Never look through a camera, binoculars or telescope unless a suitable solar filter is securely mounted on the front of the instrument.
Totality
Only observers confirmed to be inside the path of totality may remove eye protection, and only after the bright solar surface is completely covered. Put protection back on as soon as it reappears.
When in doubt
Keep the glasses on. A 99% partial eclipse is still unsafe to view directly.
Verifiable sources
These sources support the data and guidance above.