We plan to discuss the most recent findings concerning the theoretical framework adopted to model the pulsation properties of RR Lyrae stars. In particular, we will focus our attention on the topology of the RR Lyrae instability strip and on their dynamical behavior. We also discuss the use of RR Lyrae stars as helium indicators and we will outline pros and cons of the different methods. Finally, we will mention theoretical and empirical results comncerning the use of the K-band Period-luminosity relation to provide accurate distances of field and cluster RR Lyrae stars.