An assignment is a term used with similar meanings in the law of contracts and in the law of real estate. In both instances, it encompasses the transfer of rights held by one party - the assignor - to another party - the assignee. The legal nature of the assignment determines some additional rights and liabilities that accompany the act.

Liabilities
Assignor remains liable unless there is an agreement to the contrary.

Continuing Liability of Assignor
Consumer Protection, Defenses and Setoffs

Liability of Assignee: generally not liable

Warranties of Assignor
Assignment of rights under a contract is the complete transfer of the rights to receive the benefits accruing to one of the parties to that contract. For example, if party A contracts with Party B to sell his car to him for $10, party A can later assign the benefits of the contract - the right to be paid $10 - to party C. In this scenario, party A is the obligee/assignor, party B is an obligor, and party C is the assigneee. Such an assignment may be donative (essentially given as a gift), or it may be contractually exchanged for consideration. It is important to note, however, that party C is not a third party beneficiary, because the contract itself was not made for the purpose of benefitting party C. However an Assignment only transfers the rights/benefits to a new owner. The obligations remain with the previous owner. Compare Novation.

Assignment of contract rights
The common law favors the freedom of assignment, so an assignment will generally be permitted unless there is an express prohibition against assignment in the contract. Where assignment is thus permitted, the assignor need not consult the other party to the contract. An assignment cannot have any effect on the duties of the other party to the contract, nor can it reduce the possibility of the other party receiving full performance of the same quality. Certain kinds of performance, therefore, cannot be assigned, because they create a unique relationship between the parties to the contract. For example, if party A contracts to hire an attorney to represent her in a civil case for a fee of $1000, she cannot then assign her contractual right to legal representation to another party. Note however, that party A can assign her right to sue under the same claim she contracted with the attorney to pursue.

When assignment will be permitted
For assignment to be effective, it must occur in the present. No specific language is required to make such an assignment, but the assignor must make some clear statement of intent to assign clearly identified contractual rights to the assignee. A promise to assign in the future has no legal effect. Although this prevents a party from assigning the benefits of a contract that has not yet been made, a court of equity may enforce such an assignment where an established economic relationship between the assignor and the assignee raised an expectation that the assignee would indeed form the appropriate contract in the future.
A contract may contain a non-assignment clause, which prohibits the assignment of specific rights, or of the entire contract, to another. However, such a clause does not necessarily destroy the power of either party to make an assignement. Instead, it merely gives the other party the ability to sue for breach of contract if such an assignment is made. However, an assignment of a contract containing such a clause will be ineffective if the assignee knows of the non-assignment clause, or if the non-assignment clause specifies that "all assignments are void".
Two other techniques to prevent the assignment of contracts are recission clauses or clauses creating a condition subsequent. The former would give the other party to the contract the power to rescind the contract if an assignment is made; the latter would rescind the contract automatically in such circumstances.

Requirements for an effective assignment
There are certain situations in which the assignment must be in writing.
For more information about contractual writing requirements see Statute of frauds.

Assignment of wages
Assignment of any interest in real property
Assignment of choses of action worth over $5,000
Assignment as collateral for a loan or debt Revocability
A cause of action for breach on the part of the obligor lie with the assignee, who will hold the exclusive right to commence a cause of action for any failure to perform or defective performance. At this stage, because the assignee "stands in the shoes" of the assignor, the obligor can raise any defense to the contract that the obligor could have raised against the assignor. Furthermore, the obligor can raise against the assignee counterclaims and setoffs that the obligor had against the assignor. For example, suppose that A makes a contract to paint B's house in exchange for $500. A then assigns the right to receive the $500 to C, to pay off a debt owed to C. However, A does such a careless job painting the house that B has to pay another painter $400 to correct A's work. If C sues B to collect the debt, B can raise his counterclaim for the expenses caused by the poor paint job, and can reduce the amount owed to C by that $400, leaving only $100 to be collected.
When the assignor makes the assignment, he makes with it an implied warranty that the right to assign was not subject to defenses. If the contract had a provision that made the assignment ineffective, the assignee could sue the assignor for breach of this implied warranty. Similarly, the assignee could also sue under this theory if the assignor wrongfully revoked the assignment.

Breach and defenses
Occasionally, an unscrupulous assignor will assign the exact same rights to multiple parties (usually for some consideration). In that case, the rights of the assignee depend on the revocability of the assignment, and on the timing of the assignments relative to certain other actions.
In a quirk left over from the common law, if the assignment was donative, the last assignee is the true owner of the rights. However, if the assignment was for consideration, the first assignee to actually collect against the assigned contract is the true owner of the rights. Under the modern American rule, now followed in most U.S. jurisdictions, the first assignor with equity (i.e. the first to have paid for the assignment) will have the strongest claim, while remaining assignees may have other remedies. In some countries, the rights of the respective assignees are determined by the old common law rule in Dearle v Hall.

Earlier donative assignees for whom the assignment was revocable (because it had not been made irrevocable by any of the means listed above) have no cause of action whatsoever.
Earlier donative assignees for whom the assignment was made irrevocable can bring an action for the tort of conversion, because the assignment was technically their property when it was given to a later assignee.
Later assignees for consideration have a cause of action for breaches of the implied warranty discussed above. Successive assignments
A parallel concept to assignment is delegation, which occurs when one party transfers his duties or liabilities under a contract to another. A delegation and an assignment can be accomplished at the same time, although a non-assignment clause also bars delegation.

Assignment of property rights
A person can also assign their rights to receive the benefits owed to a partner in a partnership. However, the assignee can not thereby gain any of the assignor's rights with respect to the operation of the partnership. The assignee may not vote on partnership matters, inspect the partnership books, or take possession of partnership property; rather, the assignee can only be given the right to collect distributions of income. If the partnership is dissolved, the assignee can also claim the assignor's share of any distribution accompanying the dissolution.