An isolated portion of living tissue that is joined to another tissue, either in the same or a different organism, the consequent growth resulting in fusion of the tissues. (The word is also used for the process of joining the tissues.)

Grafting of plant tissues is a horticultural practice used to propagate plants, especially certain bushes and fruit trees, artificially. A shoot or bud of the desired variety (the scion) is grafted onto a rootstock of either a common or a wild related species (the stock). This procedure thus combines the desirable characteristics of the scion (e.g. flower form or fruit yield) with those of the stock (e.g. disease or drought resistance), and the scion supplies the stock with food made by photosynthesis. The stock supplies the scion with water and mineral salts and affects only the size and vigour of the scion.

Animal and human grafts are used to replace faulty or damaged parts of the body. An autograft is taken from one part of the body and transferred to another part of the same individual, e.g. a skin graft used for severe burns. An allograft (homograft) is taken from one individual (the donor) and implanted in another of the same species (the recipient), the process being known as transplantation, e.g. a heart or kidney transplant. In such cases the graft may be regarded by the body as foreign (a state of incompatibility): an immune response follows and the graft is rejected (see also histocompatibility).