Six years after the first 2009 summit in Yekaterinburg, the BRICS grouping of Brazil, Russia, India, China and South Africa has established its identity as an informal global governance forum. The members have consistently consolidated their cooperation, expanded and deepened their agenda, coordinated efforts aimed at the recovery and growth of their economies, and engaged with other international organizations. This work continued during the Russian presidency in 2015. This article focuses on one dimension of BRICS performance: its engagement with international organizations. Atleast three reasons define the relevance of this analysis. First, since its launch the BRICS members collectively committed tobuilding a multipolar, fair and democratic world order, which would not be possible without cooperating with key international organizations. Second, the objective of enhancing the sustainability, legitimacy and effectiveness of the global governance architecture defines the need for the flexible combination of different models of engagement of summit institutions with other international institutions. Third, according to Russia’s BRICS Presidency Concept, one of its priorities was to transition to a qualitatively new level of engagement with international organizations.The analytical framework for this study thus builds on the theory of rational choice institutionalism. The calculus approach fits the analysis of summit institutions bringing together states from a wide range of cultures, continents and economic development. Its distinctive features clearly apply to the analysis of the origin and performance of the BRICS. First, members act in a highly strategic manner to attain their priorities. Second, summitry presents an arrangement where strategic interaction among leaders plays a major role in determining political outcomes. Third, rational choice institutionalism offers the greatest analytical leverage to settings where consensus among actors accustomed to strategic action and of roughly equal standing is necessary to secure institutional changes – the features typical of summit institutions. Fourth, the institutions are created by the voluntary agreement of the leaders to perform specific functions and missions. In order to maximize benefits from the new arrangement, the founders may choose to engage voluntarily with existing institutions in a mode they regard most efficient for achieving their goals. The choice of partner institutions, modes and intensity of engagement is accepted to be strategic, intentional and voluntary, aiming to compensate for efficiency. The models of engagement are not mutually exclusive but coexist, with their choice dependent on the policy area and type of organization. The models of engagement with the other international organizations reflected in the leaders’ discourse are expected to indicate their place and role in the architecture of global governance, imputed to them at the summit’s launch and subsequent evolution.This study applies qualitative and quantitative methods. Drawing on a content analysis of BRICS documents, it tracks the dynamics of engagement with multilateral organizations and main models of engagement, comparing them with previous summits. Findings confirm the hypotheses that the choice of engagement model reflects the forum’s role and place in the global governance architecture and depends on the policy area and phase in cooperation development and perception of the organization’s relevance to BRICS objectives. The models are not mutually exclusive, but coexist, and transform in the course of cooperation. By establishing new institutions, the BRICS consolidates its cooperation with other organizations in a policy area. Engagement with the UN institutions and the World Trade Organization is based on the model of catalytic influence (exerting an influence for international organizations’ changes through endorsement or stimulus, or compelling them to reform), whereas with the Group of 20, the model of  “governance in alliance with multilateral institutions” has remained unrealized. In 2015 BRICS consolidated its preference in favour of two models: “catalytic influence” and “parallel treatment” (the creation of the forum’s own institutions). The BRICS continues to establish new institutions. While strengthening its own institutions, the BRICS will apply the model of governance in alliance with multilateral institutions to its cooperation with relevant international organizations.