We discuss the time-dependent interferences between K(L) and K(S) in t
he decays in 3pi and pipigamma, to be studied at interferometry machin
es such as the phi factory and CERN LEAR. We emphasize the possibiliti
es and the advantages of using interferences, in comparison with width
measurements, to obtain information both on CP-conserving and CP-viol
ating amplitudes. Comparison with present data and suggestions for fut
ure experiments are made.