What is Assignment?

Legal Definition
An assignment (Latin cessio) 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. It can also be a transfer of a benefit, including an equitable interest, according to established rules (at Common Law or in Equity). The rights may be vested or contingent. The details of the assignment determines some additional rights and liabilities (or duties).

Typically a third-party is involved in a contract with the assignor, and the contract is in effect transferred to the assignee. For example, a borrower borrows money from a local bank. The local bank receives a mortgage note and can thereafter transfer that note to a financial institution in exchange for a lump-sum of cash, thereby assigning the right to receive payment from the borrower to another entity. Mortgages and lending contracts are relatively amenable to assignment since the lendor's duties are relatively limited; other contracts which involve personal duties such as legal counsel may not be assignable.

The related concept of novation is not assignment; rather than assigning only the rights to another party, novation involves the replacement of the original party with a new party or the replacement of the original contract with a new contract. Since novation creates a new contract, it requires the consent of all parties whereas assignment does not require the consent of the nonassigning party, although in the case of assignment the consent of the nonassigning party may be required through a contractual provision.
-- Wikipedia
Legal Definition
Contracts. In common parlance this word signifies the transfer of all kinds of property, real, personal, and mixed, and whether the same be in possession or in action; as, a general assignment. In a more technical sense it Is usually applied to the transfer of a term for years; but it is more properly used to signify a transfer of some particular estate or interest in lands.

2. The proper technical words of an assignment are, assign, transfer, and set over; but the words grant, bargain, and sell, or any other words which will show the intent of the parties to make a complete transfer, will amount to an assignment.

3. A chose in action cannot be assigned at law, though it may be done in equity; but the assignee takes it subject to all the equity to which it was liable in the hands of the original party. 2 John. Ch. Rep. 443, and the cases there cited. 2 Wash. Rep. 233.

4. The deed by which an assignment is made,, is also called an assignment. Vide, generally, Com. Dig. h. t.; Bac. Ab. h. t. Vin. Ab. h. t.; Nelson's Ab. h. t.; Civ. Code of Louis. art. 2612. In relation to general assignments, see Angell on Assignments, passim; 1 Hate & Wall. Sel. Dec. 78-85.

5. By an assignment of a right all the accessories which belong to it, will pass with it as, if the assignor of a bond had collateral security, or a lien on property, the collateral security and the lien will pass with the assignment of the bond. 2 Penn. 361; 3 Bibb, 291; 4 B. Munroe, 529; 2 Drev. n. 218; 1 P. St. R. 454. 6. The assignment of a thing also carries with it all that belongs to it by right of accession; if, therefore, the thing produce interest or rent, the interest or the arrearages of the rent since the assignment, will belong to the assignee. 7 John. Cas. 90 6 Pick. 360.
-- Bouviers Law Dictionary
Legal Definition
In contracts. 1. The act by which one person transfers to another, or causes to vest in that other, the whole of the right, interest, or property which he has in any realty or personalty, in possession or in action, or any share, interest, or subsidiary estate therein. Seventh Nat. Bank v. Iron Co. (C. C.) 35 Fed. 440; Haug v. Riley, 101 Ga. 372, 29 S. E. 44, 40 In In A. 244. More particularly, a written transfer of property, as distinguished from a transfer by mere delivery.

2. In a narrower sense, the transfer or making over of the estate, right, or title which one has in lands and tenements; and, in an especially technical sense, the transfer of the unexpired residue of a term or estate for life or years. Assignment does not include testamentary transfers. The idea of an assignment is essentially that of a transfer by one existing party to another existing party of some species of propertv or valuable interest, except in the case of an executor. Hight v. Sackett, 34 N. Y. 447.

3. A transfer or making over by a debtor of all his property and effects to one or more assignees in trust for the benefit of his creditors. 2 Story, Eq. Jur. § 1036.

4. The instrument or writing by which such a transfer of property is made.

5. A transfer of a bill, note, or check, not negotiable.

6. In bankruptcy proceedings, the word designates the setting over or transfer of the bankrupt's estate to the assignee.
See also
-- Black's Law Dictionary
Legal Definition
A transfer. See 7 Am. St. Rep. 331.
-- Ballentine's Law Dictionary