A growing number of applications store and analyze graph-structured data. These applications impose challenging infrastructure demands due to a need for scalable, high-throughput, and low-latency graph processing. Existing state-of-the-art storage systems and data processing systems are limited in at least one of these dimensions, and simply layering these technologies is inadequate.We present Concerto, a graph store based on distributed, in-memory data structures. In addition to enabling efficient graph traversals by co-locating graph nodes and associated edges where possible, Concerto provides transactional updates while scaling to hundreds of nodes. Concerto introduces graph views to denote sub-graphs on which user-defined functions can be invoked. Using graph views, programmers can perform event-driven analysis and dynamically optimize application performance. Our results show that Concerto is significantly faster than in-memory MySQL, in-memory Neo4j, and GemFire for graph insertions as well as graph queries. We demonstrate the utility of Concerto’s features in the design of two real-world applications: real-time incident impact analysis on a road network and targeted advertising in a social network.