Who / Whom

"Who" and "whom" and "whose" are pronouns, which are used in place of nouns.

(Wow! The sentence above not only defines relative clauses but it HAS a relative clause!)

"Who" is used in the place of the subject of the relative clause.

"Whom" is used in the place of the object of the relative clause.

"Whose" is used to show possession

So if we were to combine the following sentences...

Example: The scientist is well known for her research. We met her yesterday.

(In the second sentence, "her" is the object, so we use "whom" to combine them.)

The scientist whom we met yesterday is well known for her research.

Example: The students missed the assignment. They were absent from class.

(In the second sentence, "they" is the subject, so we use "who" to combine them.)

The students who were absent from class missed the assignment.

Example: I explained my absence to the teacher. I had missed his class.

I explained my absence to the teacher whose class I missed.

Now do some in pairs:

The young women are from Japan. We met them at the meeting.

The man gave me good advice. I spoke to him.

Yesterday, I ran into an old friend. I hadn’t seen him for years.

The instructor gives difficult tests. I failed her course.

The woman sang a lovely song. She had many talents.

Now do some alone...

The man is standing over there. I was telling you about him.

The secretary can give you the information. She sits at the first desk.

The students raised their hands. Their names were called.

The girl was very helpful. She explained the chemistry formula to me.

The student is in one of my classes. You just met her parents.

I talked to the child. His father is the mayor of the city.

Go here for more explanation of when to use who and when to use whom.

Here are some websites to help you understand when to use one or the other: