Certificateless cryptography achieves the best of the two worlds: it inherits from identity-based techniques a solution to the certificate management problem in public-key encryption, whilst removing the secret key escrow functionality inherent to the identity-based setting. Signcryption schemes achieve confidentiality and authentication simultaneously by combining public-key encryption and digital signatures, offering better overall performance and security. In this paper, we introduce the notion of certificateless signcryption and present an efficient construction which guarantees security under insider attacks, and therefore provides forward secrecy and non-repudiation. The scheme is shown to be secure using random oracles under a variant of the bilinear DiffieHellman assumption. Keywords. Certificateless Cryptogrpahy, Signcryption, Insider Security, Non-Repudiation, Forward Secrecy, Randomness Reuse.