Rules for capital letters

People's (job) titles
Civil, religious, military and professional titles of office which precede someone's name always start with a capital letter. These indicate that someone has a certain importance in society, but they shouldn't be over-used.

• Presiding over the case was Judge Prendergast, who was in charge of the entire day's proceedings.
• Helen Clarke's husband is Doctor Peter Davis.

General titles (not indicating a specific person)
Don't use capitals for general titles. When a title of office does not directly refer to a particular person, but rather is used generally, it is not capitalized. For example, Professor (as part of someone's title) should have a capital, but 'professor' may also be a common noun and (in that context) does not need a capital.

• Helen Clarke's husband is a doctor who is currently also a professor in medical sociology.
• Presiding over the case was Judge Prendergast, who gained notoriety as the judge who rewrote New Zealand history.
• Prime Minister Helen Clark was the first elected female prime minister in New Zealand.

Be a little careful. A title may still occasionally be capitalized when not directly referring to a person when it relates implicitly to the person with that particular title.

• The key will be handed to the Prime Minister by the Queen's representative and then Parliament is declared open.
• The President walked into the White House and was immediately surrounded by photographers.