Lieutenant (junior grade), commonly abbreviated as LTJG or, historically, Lt. (j.g.)

(as well as variants of both abbreviations), is a junior commissioned officer rank of the United States Navy, the United States Coast Guard, the United States Public Health Service Commissioned Corps, and the National Oceanic and Atmospheric Administration Commissioned Officer Corps (NOAA Corps).

DOPMA guidelines suggest all "fully qualified" ensigns should be promoted to LTJG.

The time for promotion to LTJG is a minimum of two years after commissioning in the Navy or 18 months in the Coast Guard.

Lieutenants, junior grade typically lead petty officers and non-rated personnel, unless assigned to small aircraft or on staff duty.