Receptors and proteins are overexpressed in many human cancer cell membranes rather than normal tissues and are considered as the main molecular targets. Specific tumor- targeting molecules which have high affinity for these receptors can be valuable tools as carrier molecules for targeted cancer therapy and imaging. Pharmacokinetics and bioavailability of diagnostic and therapeutic agents are very important. Poor selectivity of cancer therapeutic agents causes toxicity on normal cells that limits maximum effective dose. The Attachment of these agents to macromolecules or their installation on carriers is currently under investigation. This article presents recent developments in the field of targeting agents and introduces different carriers and their applications in the diagnosis and treatment of cancer.