The present status of theoretical and experimental research on the superfluidity of helium II near the $\lambda$ point is outlined. Attention is focused on the state of the phenomenological $\Psi$ theory of superfluidity. Questions concerning the applicability limits of this theory and its underlying assumptions are discussed. Results found through the solution of several problems are discussed. Experimental data are also discussed. The need for a further comparison of theory and experiment and the actual feasibility of such a comparison are emphasized. The relationship with other approaches is pointed out.