  The CKM matrix, V, relates the quark mass and flavor bases. In the standard
model, V is unitary 3X3, and specified by four arbitrary parameters, including
a phase allowing for $CP$ violation. We review the experimental determination
of V, including the four parameters in the standard model context. This is an
active field; the precision of experimental measurements and theoretical inputs
continues to improve. The consistency of the determination with the standard
model unitarity is investigated. While there remain some issues the overall
agreement with standard model unitarity is good.
