The Solar system is the seat of many interactions between the Sun, the planets and their natural satellites. Moreover, since 1995, a large number of extrasolar planetary systems has been discovered where planets orbit around other stars, sometimes very close to them. Therefore, in such systems, tidal interactions are one of the key mechanisms that must be studied to understand the celestial bodies' dynamics and evolution. Indeed, tides generate displacements and flows in planetary (and in the host star) interiors. The associated kinetic energy is then dissipated into heat because of internal friction processes. This leads to secular evolution of orbits and of spins with characteristic time-scales that are intrinsically related to the properties of dissipative mechanisms, those latters depending both on the internal structure of the studied bodies and on the tidal frequency. This lecture is aimed to review the must advanced theories to study tidal dynamics in planetary systems and the different tidal flows or displacements that can be excited by a perturber, the conversion of their kinetic energy into heat, the related exchanges of angular momentum, and the consequences for systems evolution.