Principal Private Secretary

In the British Civil Service and Australian Public Service the Principal Private Secretary is the civil servant who runs a cabinet minister's private office. Persons holding this office in New Zealand go by the title Senior Private Secretary. The role can be a political appointment or a civil service position.

In India Principal Private Secretary is a group A Gazetted Level officer that generally take care of office of Additional Secretary to Govt of India.

Senior Principal Private Secretary (Senior PPS) is a Senior Group A Gazetted Selection Post One Rank Above Principal Private Secretary that take care of office of Secretary to Govt of India or the Equivalent Rank officer Member CBEC or Member Railway Board.

P.S.O is Principal Staff Officer is a Senior Group A Gazetted Selection Post One Rank Above Senior Principal Private Secretary that take care of office of Secretary to Govt of India or the Equivalent Rank officer Member CBEC or Member Railway Board or the Chairman. Pay Scale is equivalent to Director to Govt of India.

For More Information visit official Govt of India Website.

http://persmin.gov.in/dopt_csdivision_index.asp

http://www.archive.india.gov.in/knowindia/profile.php?id=32

A classic explanation is provided in the British sitcom Yes Minister.

Hacker: Who else is in this department?
Sir Humphrey: Well briefly, sir, I am the Permanent Under-Secretary of State, known as the Permanent Secretary. Woolley here is your Principal Private Secretary. I too have a Principal Private Secretary and he is the Principal Private Secretary to the Permanent Secretary. Directly responsible to me are ten Deputy Secretaries, 87 Under Secretaries and 219 Assistant Secretaries. Directly responsible to the Principal Private Secretaries are plain Private Secretaries, and the Prime Minister will be appointing two Parliamentary Under-Secretaries and you will be appointing your own Parliamentary Private Secretary.
Hacker: Can they all type?
Sir Humphrey: None of us can type. Mrs MacKay types: she's the secretary.
Hacker: Pity, we could have opened an agency.
Sir Humphrey: Very droll, Minister.
Hacker: I suppose they all say that, do they?
Sir Humphrey: Certainly not Minister. Not quite all..."

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Wikipedia