The enlargement of the Association of Southeast Asian Nations is the process of expanding the Association of Southeast Asian Nations (ASEAN) through the accession of new member states. This process began with ASEAN's five original members, who founded the association through the signing of the Bangkok Declaration in 1967. Since then, ASEAN's membership has grown to eleven, most recently with the accession of Cambodia in 1999 and Timor-Leste in 2025.

Currently, two states are seeking accession to ASEAN: Papua New Guinea and Bangladesh.Somare seeks PGMA's support for PNG's ASEAN membership bid Retrieved 8 July 2009

Criteria

The ASEAN Charter defines the following criteria for membership:

The state must be geographically located in Southeast Asia. The state must be recognised by all ASEAN member states. The state must agree to be bound by the ASEAN Charter. The state must be able and willing to carry out the obligations of membership.

One of the obligations of membership is that a prospective member must agree to subscribe or accede to all the treaties, declarations and agreements in ASEAN, starting with those outlined in the Bangkok Declaration of 8 August 1967 and those elaborated and developed in various subsequent treaties, declarations and agreements of ASEAN. One common concern that must be addressed through negotiations is the ability of a prospective member to participate in ASEAN Free Trade Area and all other economic co-operation arrangements. One important means of orientation for a prospective member is its attendance at ASEAN meetings and participation in co-operation projects.Preparations for the Membership of ASEAN Retrieved 14 May 2011 Other obligations of membership are that a state must maintain embassies in all current member countries of the bloc,Aquino to back East Timor's bid for ASEAN membership Retrieved 14 May 2011 and the country must attend all ministerial meetings and summits.

The Bangkok Declaration lays down no conditions for membership other than location in Southeast Asia and the usual principles of inter-state relations. ASEAN has no membership criteria related to the character of government, ideological system and orientation, economic policy, or level of development. If there were such criteria for membership, a regional association would not be possible in Southeast Asia, given its diversity.Severino, Rodolfo (2006) Southeast Asia in search of an ASEAN community: insights from the former ASEAN secretary-general, Institute of Southeast Asian Studies.

ASEAN senior officials agreed in 1983 that observer status should be granted only to potential members of ASEAN who satisfy the criteria set for ASEAN membership.

Criteria for ASEAN Regional Forum

ASEAN Regional Forum (ARF), the multilateral dialogue among Asia Pacific countries is aimed for fostering dialogue and consultation, also promoting confidence-building and preventive diplomacy throughout the region.About Us , ASEAN Regional Forum official website . Retrieved 12 June 2006. The membership criteria for ARF, as well as other Dialogue Partners, were outlined during the second ARF in 1996, in Jakarta, Indonesia. ARF ministers adopted the criteria that ARF participants must be sovereign states, which, at China's behest, was evidently meant to exclude Taiwan. They must "abide by and respect fully the decisions and statements already made by the ARF". The criteria stress that ASEAN members "automatically" take part in the ARF.

Historical enlargements

Founding members ASEAN was established on 8 August 1967, when foreign ministers of five countries – Indonesia, Malaysia, the Philippines, Singapore, and Thailand – met at the Thai Department of Foreign Affairs building in Bangkok and signed the ASEAN Declaration, more commonly known as the Bangkok Declaration. The five foreign ministers: Adam Malik of Indonesia, Narciso Ramos of the Philippines, Abdul Razak of Malaysia, S. Rajaratnam of Singapore, and Thanat Khoman of Thailand are considered as the organisation's Founding Fathers.

Continued expansion During the 3rd ASEAN Ministerial Meeting (AMM) held on 16–17 December 1969 at Cameron Highlands, Malaysia invited South Vietnam and the Kingdom of Laos to become an observer state of the new organization. South Vietnam, eyeing for full membership, has since sent participants to the ASEAN Ministerial Meetings from 1969, 1971, and 1972 as an observer until they were taken over by North Vietnam under the fall of Saigon.

At the 5th ASEAN Ministerial Meeting (AMM) at Singapore, Lon Nol's Khmer Republic became an observer at ASEAN under the invitation of Lee Kuan Yew. ASEAN brought Indochinese states into its Ministerial Meetings as observers while discussing ZOPFAN and regional security. Khmer's observer role effectively ended with the fall of Phnom Penh in 1975. In 1976, the Melanesian state of Papua New Guinea was accorded observer status. The bloc then grew when Brunei Darussalam became the sixth member after it joined on 8 January 1984, barely a week after the country became independent on 1 January.

In 1992, at the 4th ASEAN Summit and the subsequent 25th AMM, Vietnam joined the Treaty of Amity and Cooperation and became an ASEAN observer, then from 1993 it began regular participation in ASEAN foreign ministers’ meetings and sectoral cooperation. Vietnam would later became the seventh full member on 28 July 1995.

Laos, Myanmar, and Cambodia The next three members of ASEAN began their application in joining the bloc in the 1990s.

Laos became an ASEAN observer at the 25th ASEAN Ministerial Meeting (AMM) in Manila, Philippines, in July 1992. At the 28th AMM in Bandar Seri Begawan, Brunei, the Lao foreign minister announced that he wished to see Laos join ASEAN in 1997, stated in a letter of application for membership dated 15 March 1996.

Cambodia was accorded observer status at the 28th AMM in July 1995. The Cambodian foreign minister applied for membership in a letter dated 23 March 1996. Like Laos, Cambodia also wished to join ASEAN in 1997.

The foreign minister of Myanmar attended the 27th and 28th AMM as a guest of the host governments. During the 28th meeting, Myanmar acceded to the Treaty of Amity and Cooperation in Southeast Asia and applied for observer status.

The heads of government of Myanmar, Laos and Cambodia met with those of ASEAN during the Fifth ASEAN Summit in Bangkok on 15 December 1995. The representative of Myanmar expressed hope that his country would be accorded observer status at the 29th AMM in 1996.

The ASEAN Security Committee (ASC) established a working group, chaired by ASEAN Deputy Secretary-General Mr. Mahadi Haji Wasli, to look into all issues on the potential membership of Cambodia and Laos. On 17 July 1996, the working group held consultations with the director-general of the ASEAN Department of Laos in Jakarta.

At the 29th AMM, Myanmar was accorded observer status, and participated in the ARF for the first time. On 12 August 1996, Myanmar submitted application for membership in ASEAN, with hopes for joining by 1997 along with Cambodia and Laos. The ASC then extended the mandate of the Working Group on the Membership of Cambodia and Laos to also include the membership of Myanmar.

Laos and Myanmar became members of ASEAN on 23 July 1997. Cambodia's membership was deferred due to the country's internal political struggle; following the stabilisation of its government, Cambodia joined on 30 April 1999.

In addition to the growth in membership, the bloc experienced a drive for further integration in the 1990s. In 1990, Malaysia proposed the creation of an East Asia Economic CaucusEast Asia Economic Caucus . ASEAN Secretariat. Retrieved 14 March 2007. composing the then-members of ASEAN and the People's Republic of China, Japan, and South Korea, with the intention of counterbalancing the growing influence of the United States in the Asia-Pacific Economic Cooperation (APEC) and in the Asian region as a whole.UNT.edu, Asia's Reaction to NAFTA, Nancy J. Hamilton. CRS - Congressional Research Service. Retrieved 14 March 2007. This proposal failed, however, due to heavy opposition from the United States and Japan., Whither East Asia? Retrieved 14 March 2007.IHT.com, Japan Straddles Fence on Issue of East Asia Caucus. International Herald Tribune. Retrieved 14 March 2007. Despite this failure, member states continued to work for further integration and ASEAN Plus Three was created in 1997.

In 1992, the Common Effective Preferential Tariff (CEPT) scheme was signed as a schedule for phasing tariffs and as a goal to increase the "region's competitive advantage as a production base geared for the world market". This law acted as the framework for the ASEAN Free Trade Area. After the 1997 Asian financial crisis, a revival of the Malaysian proposal was established in Chiang Mai, known as the Chiang Mai Initiative, which calls for better integration between the economies of ASEAN and the ASEAN Plus Three countries.

Timor-Leste

In March 2011 Timor-Leste submitted a membership application to ASEAN, a move which was supported by Indonesia, its former colonialist turned partner-ally, and the Philippines, its only Catholic ally in Asia.

Timor-Leste regained its independence in 2002, and from the following year took part in the Southeast Asian Games, a multi-sport event associated with ASEAN. In 2005, the country became the 25th to join the ARF. The biggest struggle toward joining ASEAN was for the young and war-torn country to maintain embassies in all ten ASEAN member countries. Timorese President José Ramos-Horta hoped to gain membership before 2012.

Lack of consensus prevented ASEAN from arriving at decisions on observer status for Timor-Leste and its accession to the Treaty of Amity and Cooperation. The treaty makes clear distinctions between the rights of regional and non-regional signatories, but whether Timor-Leste a part of the region is debatable.

Singaporean Prime Minister Lee Hsien Loong objected in late 2011 to Timor-Leste's membership, due to his desire to achieve economic integration by 2015, which the relatively less-developed Timor-Leste would make difficult. Some member states are concerned that, having experienced the entry of four relatively underdeveloped members, ASEAN would be admitting an even poorer one. Although ASEAN has no membership criteria regarding political ideology, some ASEAN countries had difficulties with Timor-Leste's eventual membership.

In 2015, Timor-Leste's ambassador to Malaysia said the country was ready to join ASEAN, having fulfilled the two major requirements of being located in the region and having opened embassies in ASEAN member countries. In 2016, Indonesia announced that Timor-Leste's membership bid could be realised in 2017, since the feasibility studies conducted by both countries on Timor-Leste's stability, security, economy, and culture would be finished by the end of 2016. The Philippines, a close ally of Timor-Leste, would be the ARF host for 2017.

In November 2022, following the 40th and 41st ASEAN Summit in Phnom Penh, the organisation issued a statement announcing that it had agreed "in principle" to East Timor's membership, granted East Timor observer status at high-level meetings and that a roadmap to full membership would be submitted at the 2023 summit. At the 42nd ASEAN Summit in Labuan Bajo in May 2023 the roadmap for Timor Leste's accession was adopted.