In this paper, we propose an efficient multi-receiver identity based signcryption scheme which only needs one pairing computation to signcrypt a message for n receivers and can provide confidentiality and authenticity simultaneously in the multi-receiver setting. We compare our scheme with several multi-receiver constructions from the security and efficiency points of view and argue that our provably secure scheme is more efficient than other known constructions. To address the security issues, we formulate security models and define strong security notions for multi-receiver identity based signcryption schemes. We also prove that our scheme satisfies these strong security requirements in the random oracle model.