What is Accession?

Legal Definition
Accession has different definitions depending upon its application.

In property law, it is a mode of acquiring property that involves the addition of value to property through labor or the addition of new materials. For example, a person who owns a property on a river delta also takes ownership of any additional land that builds up along the riverbank due to natural deposits or man made deposits.

In commercial law, accession includes goods that are physically united with other goods in such a manner that the identity of the original goods is not lost. In English common law, the added value belonged to the original property's owner. For example, if the buyer of a car has parts added or replaced, then the buyer fails to make scheduled payments and the car is repossessed, the buyer has no right to the new parts because they have become a part of the whole car.

In modern common law, if the property owner allows the accession through bad faith, the adder of value is entitled to damages or title to the property. If the individual who adds value to the owner's chattel (personal property) is a trespasser or does so in bad faith, the owner retains title and the trespasser cannot recover labor or materials. The owner of the chattel may seek conversion damages for the value of the original materials plus any consequential damages. Alternatively, the owner may seek replevin (return of the chattel). However, the owner may be limited to damages if the property has changed its nature by accession. For example, if a finder discovers a gemstone and in good faith believes it to be abandoned and then cuts it and integrates it into a work of art, the true owner may be limited to recovery of damages for the value of the gemstone, but not of the final art piece by way of replevin. The remedies and application of the law vary by legal jurisdiction.
-- Wikipedia
Legal Definition
1) In trusts and estates law, assets produced by a devised asset after the execution of a will.

2) In secured transactions law, goods that physically united with other goods in a way that doesn't lose the identity of the original goods. Compare with commingled goods.
Legal Definition
Property. The ownership of a thing, whether it be real or personal, movable or immovable, carries with it the right to all that the thing produces, and to all that becomes united to it, either naturally or artificially; this is called the right of accession.

2. – 1. The doctrine of property arising from accession, is grounded on the right of occupancy.

3. – 2. The original owner of any thing which receives an accession by natural or artificial means, as by the growth of vegetables, the pregnancy of animals; Louis. Code, art. 491; the embroidering of cloth, or the conversion of wood or metal into vessels or utensils, is entitled to his right of possession to the property of it, under such its state of improvement; 5 H. 7, 15; 12 H. 8, 10; Bro. Ab. Propertie, 23; Moor, 20; Poph. 88. But the owner must be able to prove the identity of the original materials; for if wine, oil, or bread, be made out of another man's grapes, olives, or wheat, they belong to the new operator, who is bound to make satisfaction to the former proprietor for the materials which he has so converted. 2 Bl. Com. 404; 5 Johns. Rep. 348; Betts v. Lee, 6 Johns. Rep. 169; Curtiss v. Groat, 10 Johns. 288; Babcock v. Gill, 9 Johns. Rep. 363; Chandler v. Edson, 5 H. 7, 15; 12 H. 8, 10; Fits. Abr. Bar. 144; Bro. Abr. Property, 23; Doddridge Eng. Lawyer, 125, 126, 132, 134. See Adjunction; Confusion of Goods. See Generally, Louis. Code, tit. 2, c. 2 and 3.
-- Bouviers Law Dictionary
Legal Definition
International law, is the absolute or conditional acceptance by one or several states, of a treaty already concluded between one or several states, of a traty already concluded between other sovereignties. Merl. Rep. mot Accession.
-- Bouviers Law Dictionary
Legal Definition
The right to all which one's own property produces, whether that property be movable or immovable; and the right to that which is united to it by accession, either naturally or artificially. 2 Kent, 360 ; 2 Bl. Comm. 404. A principle derived from the civil law, by which the owner of property becomes entitled to all which it produces, and to all that is added or united to it, either naturally or artificially, (that is, by the labor or skill of another,) even where such addition extends to a change of form or materials; and by which, on the other hand, the possessor of property becomes entitled to it, as against the original owner, where the addition made to it by his skill and labor is of greater value than the property itself or where the change effected in its form is so great as to render it impossible to restore it to its original shape. Burrill. Bette v. Lee, 5 Johns. (N. Y.) 348, 4 Am. Dec. 368; Lampton v. Preston, 1 J. J. Marsh. (Ky.) 454, 19 Am. 'Dec. 104; Eaton v. Munroe, 52 Me. 63; Pulcifer v. Page, 32 Me. 404, 54 Am. Dec. 582.

In international law. The absolute or conditional acceptance by one or several states of a treaty already concluded between other sovereignties. Merl. Repert. Also the commencement or inauguration of a sovereign's reign.
-- Black's Law Dictionary
Legal Definition
The addition of a lesser thing to a greater, either by nature or by man. See 24 Ky. 454, 19 Am. Dec. 104. A nation’s acceding to a treaty.
-- Ballentine's Law Dictionary