In this paper, we propose a three-parameter family of conjugate gradient me
thods for unconstrained optimization. The three-parameter family of methods
not only includes the already existing six practical nonlinear conjugate g
radient methods, but subsumes some other families of nonlinear conjugate gr
adient methods as its subfamilies. With Powell's restart criterion, the thr
ee-parameter family of methods with the strong Wolfe line search is shown t
o ensure the descent property of each search direction. Some general conver
gence results are also established for the three-parameter family of method
s. This paper can also be regarded as a brief review on nonlinear conjugate
gradient methods.