The objective of the BIG IoT project is to ignite really vibrant Internet of Things (IoT) ecosystems. We will achieve this by bridging the current interoperability gap between the vertically integrated IoT platforms and by creating marketplaces for IoT services and applications. Despite various research and innovation projects working on the Internet of Things, no broadly accepted professional IoT ecosystems exist. The reason for that are high market entry barriers for developers and service providers due to a fragmentation of IoT platforms. The goal of this project is to overcome these hurdles by Bridging the Interoperability Gap of the IoT and by creating marketplaces for service and application providers as well as platform operators. We will address the interoperability gap by defining a generic, unified Web API for smart object platforms, called the BIG IoT API. The establishment of a marketplace where platform, application, and service providers can monetize their assets will introduce an incentive to grant access to formerly closed systems and lower market entry barriers for developers. The BIG IoT consortium is well suited to reach the outlined goals, as it comprises all roles of an IoT ecosystem: resource providers (e.g., SIEMENS, SEAT), service and application developers (e.g., VODAFONE, VMZ), marketplace providers (e.g., ATOS), platform providers (e.g., BOSCH, CSI, ECONAIS), as well as end users connected through the public private partnerships of WAG and CSI or the user-focused information services that VMZ provides for the city of Berlin. The major industry players cover multiple domains, including mobility, automotive, telecommunications, and IT services. Four university departments will help to transfer the state of the art into the state of the practice and solve the open research challenges. This consortium will mobilise the necessary critical mass at European level to achieve the goals and to reach the ireach the impacts set out in this project.