The cloud computing paradigm as originally conceived has reached a plateau of evolution, exposing several limitations that compromise the main features of the paradigm: resource contention, interruption of services, lack of interoperability in data representation, quality of service degradation, and others. Consequently, several new approaches to its use and optimization have been implemented to maintain continuity of technology. In this way, multiple clouds organizations have been formed with the objective of maximizing the use of cloud computing, in particular small-and medium-sized cloud providers who present difficulties to maintain all properties of the paradigm have mobilized themselves into organizations to maximize their revenues. Such organizations, formally called inter-clouds, have been gaining attention, where solutions like hybrid clouds, multi-clouds, and cloud federations are the main elements in the academic-scientific and industrial world. In particular, cloud federations are well behaved because organizations governed by a contract can be interesting and useful in many critical environments. However, there is a lack of works dedicated only to clouds federations. In addition, the existing works are not able to describe federations as unique inter-cloud entities to highlight specific properties and characteristics. In this paper, we present the desired functional and non-functional properties for cloud federations through the identification of the main architectures in the literature and we evaluate these architectures based on the described properties. (C) 2016 Elsevier Ltd. All rights reserved.725171