Vietnam joins Brunei, Indonesia, Malaysia, the Philippines, Singapore and Thailand in a regional grouping which is actively soliciting new blood and has lined up Burma as its next member.
In historical terms this is an astonishing about face for a body created in 1967 when the Cold War was going strong and the United States was convinced that the fall of South Vietnam to the Communists would produce a domino effect, with the whole region succumbing to Communist rule.
At the time Thailand's foreign minister, Thanat Khoman, coined the term "collective political defence" to describe Asean's objectives.
Apart from Indonesia, the organisation's founding states were dependent on either Britain or the US for their defence. They were not natural allies but bound together by the fear of perceived Vietnamese and Chinese expansionist ambitions.
Fears of Vietnam have now receded and Hanoi is seen as an important ally to counterbalance China's military might. Peking has been flexing its muscles in recent months in both the Taiwan Strait (with missile testing) and the Spratly Islands.
In terms of historic distrust, the Chinese and Vietnamese have a relationship similar to that of the French and British. And since 1975 the newly united Vietnam and the victorious Communist forces in Cambodia and Laos formed a loose "militant solidarity". Asean, which they routinely described as a lackey of US imperialism, is now keen to attract them as members.
Vietnam has been struggling to come out of the diplomatic cold for the past decade. On 11 July it was finally given full diplomatic recognition by the US, opening the way for much more active participation in world bodies, notably the World Bank and the International Monetary Fund.
The emphasis of Asean's activities is now on economic cooperation. Vietnam will find it hard to be a full player as it weans itself from a centrally planned economy.
The other members have agreed to whittle away tariffs on intra-Asean trade by 2003, but Vietnam says it will not be able to reciprocate for another three years.