A written qualifying exam, at UCI called the Phase II exam.

An oral qualifying exam, at UCI called the Advancement exam.  The student writes a substantial survey of the general area in which he/she intends to do research, and presents it to his committee (advisor + 2-4 other professors, including an external member from another department). 

After passing this stage, a student is said to have "advanced to candidacy", and is a "doctoral candidate".

A preliminary oral defense of the planned research topic, here called the topic defense exam. 

Final oral defense, after writing the dissertation and (if possessed of any common sense) getting each of the committee members to read and approve it.  The candidate presents his original research to the committee as well as to any interested graduate faculty members of the university.  Usually no other faculty show up, but since the graduate faculty as a whole grants the degree, any professor is welcomed and may ask questions and offer comments (but not vote, that's just the committee). 

After this the student is traditionally addressed as Doctor and by courtesy is considered to have attained his/her Ph.D.  He/she gets the committee's signatures on (usually) the dissertation's title page.  Wise students bring several copies of the page to the defenses and get them all signed by the committee members, just in case.  One title page with signatures goes to the Graduate School, which will not grant the degree without them.  Another is traditionally bound into the dissertation copy the student presents to his/her advisor.

Getting the Graduate School editor to sign off on it.  It seems like this should be just a formality but there's always something.  My dissertation had a figure that exceeded the Grad School margin rules,  and it took about a week to get it right and get the editor to check it over again.  The day the Graduate School accepts your dissertation is the date of your degree.

Walking at Commencement in those splendid new robes, for the handshake and photos and "hooding".  The advisor traditionally "hoods" the student, putting the ornate hood of the gown over the student's head for the first time.  Congratulations!