Accurate polarization data obtained with neutrons below 20 MeV in the A ≤ 3 systems provide important new information on details of the nucleon-nucleon (NN) interaction. The two-nucleon and three-nucleon data favor the Paris potential over the new Bonn (OBEPQ) potential. However, none of the realistic potential models describes the elastic neutron-deuteron analyzing power satisfactorily. Charge independence breaking in the 3P NN interactions and/or three-body force effects must be considered. © 1989.