On the problem of quark-lepton families

The problem of quark-lepton families is discussed in the “bottom-up” phenomenological approach to the extensions of the Standard model. It provides the possibility of the {\it Horizontal unification} of the three known families on the basis of horizontal gauge flavor $SU(3{)}_H$ symmetry. The new generations of quarks and leptons can exist. If unstable and mixed with light fermions, they should contribute the CKM matrix. If stable and decoupled from known families, new generations can provide new candidates for dark matter.