The main purpose of the alliance is to consolidate the voices of Small Island Developing States (SIDS) to address global warming.

These island countries are particularly vulnerable to climate change and its related effects on the ocean, including sea level rise, coastal erosion and saltwater intrusion.

AOSIS functions primarily as an ad hoc lobby and negotiating voice for SIDS through the United Nations (UN) system.

[12] Its advocacy was instrumental to the inclusion of references to the greater vulnerability and special needs of SIDS in Article 4.8 of the UNFCCC.

[7][14] However, AOSIS was unsuccessful in its attempts to persuade nations to include commitments to specified greenhouse gas emission reduction targets in the Framework.

[20][7] The five year review of the Barbados Conference, conducted at a special session of the UN General Assembly in 1999, found that the SIDS efforts to make progress towards sustainable development had been limited,[7] while the ten year review of the Barbados Conference, which took the form of an international meeting in Mauritius in 2005, found that its implementation was largely unsuccessful.

[12] AOSIS has used formal and informal meetings scheduled in advance of UN climate change conferences to raise awareness and political momentum for its mission.

For example, in the lead up to the 2009 UN Climate Change Conference (UNFCCC) in Copenhagen, members of the cabinet of the Maldives, an AOSIS member state, held an underwater cabinet meeting to create awareness of the threat that climate change poses to the very existence of the Maldives.

reported that members from the island state of Tuvalu interrupted a session of the Conference on 10 December 2009 to demand that global temperature rise be limited to 1.5 °C instead of the proposed 2 °C.

[12] According to writer and activist Mark Lynas, the inclusion of the 1.5 °C target in the Paris Agreement was 'almost entirely' due to the advocacy of SIDS and other developing countries.

[27] At the 2013 Warsaw climate change conference, AOSIS pushed for the establishment of an international mechanism on loss and damages stressed by the wreckage of Supertyphoon Haiyan.

The results of a recent review of the literature [29] show that potential liability for climate change-related losses for AOSIS is over $570 trillion.

While AOSIS' focus is on SIDS, its membership also includes several low-lying coastal countries, for example Belize and Guyana, and larger islands, for example Papua New Guinea.

AOSIS also has five observers: American Samoa, Guam, Netherlands Antilles, Puerto Rico, and the United States Virgin Islands.