* Before a person's name: This is the most common usage. For example, "Dr. Smith" or "Dr. Jane Doe."
* In formal writing and speech: When addressing someone as "Doctor" in a formal setting, you would use the abbreviation "Dr."
* In titles and headings: If you are referring to a doctor in a title or heading, you would use "Dr."
However, there are some situations where you shouldn't abbreviate "doctor":
* When referring to a profession in general: For example, "I want to be a doctor" or "She is a doctor at the local hospital."
* When referring to a doctor by their last name alone: For example, "I saw Dr. Smith yesterday" but "I saw Smith yesterday."
* In informal writing and speech: You can use the full word "doctor" in casual conversation or writing.
Note: It's always a good idea to be aware of the context and audience when deciding whether or not to abbreviate "doctor."