Annual single number series registers of letter correspondence received by External Affairs 1903-1910 and then distributed within the Prime Minister's Office (1904-1910) and where appropriate to the six other agencies, as described in the Administrative Arrangements, dated Melbourne, 1 June 1906.

The series consists of bound lined ledgers listing incoming letters; chronologically in an annual single number sequence.  The printed column headings are:
1. Previous Papers
2. Progressive Number
3. Subsequent Papers
4. Other Department Number
5. Date of Letter/Registration
6. From whom
7. Subject of letter
8. Referred to whom/when
9. Remarks

Entries in red ink were used to alert the user to previous/subsequent correspondence for years outside the current volume being referred to. This highlighting technique is used throughout the series.  The series in its original form consisted of nine books as nine bound volumes, one for each year (except 1907 in two volumes), covering the years 1903-1910.  As a result of rebinding of these nine books by the Australian Government Publishing Service (AGPS), in October 1973, the number of items expanded to twelve.  Volume 7, 1908, was split into Parts A, B, C and the volume for 1909, into Parts A and B.  The artificial splitting of the original books has necessitated the photography and reproduction 1:1 of the final left hand page of 1908/1909 Part A volumes.  The photographed pages were bound into the beginning of Part B in both items.  In May 1973, before conservation and rebinding occurred the series was microfilmed in its entirety on silver halide base for master and duplicate copies.  In 1986 a diazo reference set was made.

The Department of External Affairs [I] from 1903-1910, was under the direct control of the Prime Minister.  Major functions listed in the Administrative Arrangements of the time include diplomatic appointments, overseas passports, immigration, emigration, aliens control and the administration of Australia's foreign territories, such as Papua and islands in the Pacific.  These functions are found throughout the inward correspondence of the series.  Where inward correspondence impinges the Ministers portfolios of Attorney General, Trade and Customs, Treasurer, Postmaster-General, Defence, Home Affairs:  these letters were registered, described and forwarded on to their relevant Minister of State's office.  This is especially evident in volume 1, 1903 where the record book provides evidence that External Affairs acted as a clearing house for all ministerial portfolios of government.  From 1904 the 'Referred to Whom' letters/correspondence annotations become less used. This perhaps reflects the establishment of a separate Prime Ministers Office (CA 588), in April 1904.

By early 1905, volume 3, applications for naturalization (domicile) certificates become a regular feature in register entries.  The only referrals in any quantity during this year are to the Treasurer. Noticeably by 1906, volume 4, no referrals are pencilled in, where obvious Defence correspondence is listed.  During this year, there is an increase in entries which relate to overseas and domestic criminal elements, concerning both aliens and residents.  Regular reference is made to Japanese seamen jumping ship, and subsequently standing trial. From 1907, volume 5 onwards the 'Destroyed' material stamp increases in frequency, Volume 7, 1908 Part B on the final page sets out 'Number of Entries 1908'.  This list tallies letter entries for each month with a running cumulative total for that year.

Incoming letters come from a wide range of correspondents from throughout Australia, spanning state and federal government to private individuals. Correspondents who regularly occur in the series include: Secretary General, Governor-General, Premiers of states and especially reports from the major port entries such as 'Collector of Customs, Brisbane'.  Many entries originate from the sub Customs Controller, Broome, reflecting this port's strong connection with importation of labour ('Asiatics') for the pearling and trepang industry. The dominant themes throughout the volumes are control of immigrants and application for domicile status into Australia.

The series ends in December 1910, prior to the creation of the Prime Ministers Department (CA 12) on 1 July 1911 by Executive Council Minute No 53 of 28 December 1911.

The Prime Minister's Department took some of the administrative functions previously carried out by Department of External Affairs, as outlined by the Administrative Arrangements Order of 13 April 1912:

1. Auditor-General and Staff
2. Communication with the Governor-General
3. Communication with the States
4. Officers of the Parliament
5. Public Service Commissioner and Staff (as from 1 July 1912) 6. Royal Commissions
7. The Commonwealth of Australia Gazette
8. The Federal Executive Council