If the contract specifically precludes assignment, the contractual right is not assignable. Whether a contract is assignable is a matter of contractual intent and one must look to the language used by the parties to discern that intent.
In Arizona, most real estate contracts are assignable unless explicitly stated otherwise in the agreement. Certain conditions may affect this, however. For example, contracts involving personal services or that require specific qualifications of the parties may not be assignable.
The assignor must agree to assign their rights and duties under the contract to the assignee. The assignee must agree to accept, or "assume," those contractual rights and duties. The other party to the initial contract must consent to the transfer of rights and obligations to the assignee.