Semper fidelis is a Latin phrase that means "always faithful" – it serves globally as a common motto for several military units.

Semper fidelis may also refer to:

Semper Fidelis (march), John Philip Sousa march

Semper Fidelis, an album by German black metal band Nargaroth

Semper Fidelis, first mission in the first-person shooter video game Battlefield 3

Semper Fidelis Marine Corps, rename of computer game Söldner: Secret Wars