The main reason why people ask if there are any differences between tenderloin and filet mignon is that both are cuts of beef from the same part of the animal body. However, one of the major differences between the two is that filet mignon is also a part of the tenderloin.
If the tenderloin is the tenderest part of a loin of meat, filet mignon is the steak cut of beef taken from the tenderloin, especially the portion of meat at the tip. What this means is that; while a tenderloin can also be called filet mignon, the latter does not have the exact meaning of what the tenderloin represents.
While you can cook the tenderloin as a whole piece without cutting into medallions, filet mignon is usually cooked by wrapping its steaks up so as to give it more flavor. In terms of size, tenderloin is usually larger than filet mignon.