Grammar Lesson: Who or Whom?

"Who" is the subject.
"Whom'' is the object.

Every verb requires a preceding subject.

Thus:

It is "Whom are you going with" and not "who are you going with" as the verb 'going' already has its subject: 'you'.

It is "Who broke the vase?" and not "whom broke the vase" as the verb 'broke' requires a subject: 'who'.

Whom always correlates to 'him, her, them, whomever'.

Who always correlates to 'he, she, they, whoever'.

Think of how a question is answered and you will know which to use.

"Whom are you going with" is correct because you wouldn't reply "I am going with she", you would say "I am going with her".