The fourth season of the American drama/adventure television series Alias premiered January 5, 2005 on ABC and concluded May 25, 2005 and was released on DVD in region 1 on October 25, 2005.

Guest stars in season four include Sônia Braga, Joel Grey, Michael McKean, Lena Olin, and Isabella Rossellini.

Only one Wednesday evening (February 2) was skipped in this run, so as not to coincide with the 2005 State of the Union Address from President George W. Bush.

A new night, new lead-in, and noticeable lack of weeks without new episode broadcasts are thought to have contributed to some of the series' best overall ratings during its five-season run.

The biological nerve agent infects Dixon as he attempted to aid the technician who was inspecting the hard drive.

Marshall, late for work, arrives at the parking lot only to be informed that they're in lockdown mode and that Sydney is trapped in a coffin somewhere in Cuba.

Over the phone, Jack instructs Marshall on how to remove the man's eyes (using a spork) so that he can access a security station in the basement and deactivate a firewall.

A strike would also release deadly radiation into the atmosphere and make Chernobyl look pale in comparison — in Jack Bristow's words, "like a kitchen fire."