Seven different activities constitute tree domestication: (1) manipula
tion of tree populations by silvicultural practices; (2) enhancement o
f site productivity; (3) control of destructive agents; (4) evolution
of trees under natural selection; (5) semi-natural selection for survi
val in the socio-agricultural circumstances in which trees are grown;
(6) conscious human selection for desired characteristics; and (7) cor
related response to selection (which usually involves reduction of tho
se plant parts that are not desired). Each of these activities is disc
ussed, and its contribution to the present makeup of tree populations
used for agroforestry is considered. Although tree domestication has b
een practiced by farmers for many centuries, selection and breeding pr
ograms for multipurpose agroforestry trees have existed for only the p
ast thirty years. Some of the problems faced by existing tree improvem
ent programs are discussed; these include: multiplicity of usable spec
ies, great demand for multipurpose trees (MPTs), existence of improvem
ent programs with few species, difficulty of combining desired traits
in a multipurpose ideotype, high cost and slow progress with present m
ethods, and the fate of improved material introduced on farms. Among t
he solutions,considered is more involvement of farmers in the process
of selection, testing, and propagation of MPTs. The possible use of sp
ecies mixtures also holds promise.