In philately, an omnibus issue is an issue of stamps by several countries with a common subject and which may share a uniform design. Omnibus issues have often been made by countries under common political control or groups of colonies due to the close co-operation required to produce the issue. Omnibus issues are to be distinguished from joint issues which are usually much smaller in scope.
The first omnibus issue
British Commonwealth issues
Omnibuses have been particularly associated with stamps from the former British Empire, now the British Commonwealth, due to the large number of territories participating. Initially designs were identical for each colony with only the values, colours and colony names varying. Over time, however, a wider range of designs has been used within the same issue. The first issue was the Silver Jubilee issue of 1935. Many others have followed, usually on themes related to the British Royal Family, but also for subjects such as Freedom from Hunger (1963) and the 1966 Football World Cup. Not every colony necessarily participates in every issue, although the revenue produced by the stamps is a valuable source of income for many smaller colonies/countries which may have few other ways of raising funds.
A list of British Omnibus issues is given below:
1935 - Silver Jubilee
1937 - Coronation
1945-1946 - Peace and Victory
1948-1949 - Silver Wedding
1949 - Universal Postal Union
1951 - University
1953 - QEII Coronation
1953 - Royal Visit
1958 - West Indies Federation
1963 - Freedom From Hunger
1963 - Red Cross Centenary
1964 - Shakespeare
1965 - International Telecommunications
1965 - International Cooperation
1966 - Churchill Memorial
1966 - Football World Cup
1966 - U.N.E.S.C.O Issue
1966 - World Health Organisation
1972 - Royal Silver Wedding
1973 - Royal Wedding Princess Anne
1974 - Churchill Centenary
1977 - Royal Silver Jubilee
1978 - 25th Anniversary of Queen Elizabeth's Coronation
1980 - Queen Mothers 80th Birthday
1981 - Charles and Diana Royal Wedding
1982 - Princess Diana 21st and other Birthdays
1985 - Life and Times of Elizabeth the Queen Mother
1990 - Queen Mother's 90th Birthday
1997 - Queen Elizabeth Golden Wedding
Other omnibus issuers
The omnibus remains popular with countries whose philatelic marketing is handled by the Inter-Governmental Philatelic Corporation as it enables those countries to market their stamps into the lucrative United States and European thematic stamp market by featuring subjects popular in those countries. These issues have, however, been criticised for not being relevant to the culture of the participating countries, for instance stamps featuring Disney characters issued by poor African countries.
While most earlier omnibus issues were genuine attempts to help a group of countries celebrate an anniversary or event, the fact that these became popular with stamp collectors tempted issuing authorities to bring out more stamps than would have otherwise been thought necessary. These were often heavily marketed. 
- Mackay, James. Philatelic Terms Illustrated. 4th edition. London: Stanley Gibbons, 2003, p.95. ISBN 0-85259-557-3.
- Sutton, R.J. & K.W. Anthony. The Stamp Collector's Encyclopaedia. 6th edition. London: Stanley Paul, 1966, p.216.
- Murray, Robert. 1981 Royal Wedding Omnibus Stamp Collection. http://www.stamp-shop.com/1981-royal-wedding.html