The present chapter aims in presenting what are tidal rhythmites (TRs), where do they preferentially deposit and are preserved, and why, and what is the information the analysis of ancient TRs may provide. TRs are made of vertically stacked sand-mud couplets that show rhythmic changes in thickness and/or shape directly related to tidal energy fluctuations and cycles, primarily neap-spring-neap cycles. They are known in modern tidal environments and recognized in rock records. TR can be considered as diagnostic sedimentary facies of internal estuarine tidal flat. Some examples are also described in deep subtidal pro-deltaic settings. Both depositional systems fulfill the conditions required for their deposition and preservation (sheltered environment, high enough sediment supply, accommodation). The recognition of TR, especially in ancient successions, is based on spectral analysis applied to couplet thickness evolution series in order to demonstrate the consistency of their cyclic nature with tidal cyclicities. As a result of these analyzes, complemented with facies description, TRs are tools to better understand ancient tidal systems. Above all, they constitute an absolute evidence of the action of tides. Such information together with spectral characteristics of the signal encoded into the studied TR, provide major constraints for paleogeographic reconstruction and modeling. The deposition and preservation of TRs allows to discuss as well about the fascinating issue of sedimentation rate and its tremendous variability in time and space. Since TR directly record Earth-Moon system dynamics, their spectral analyzes to extract ancient orbital parameters developed as soon as their earliest recognition. On this basis, curves of the lunar retreat have been proposed, from Middle Proterozoic to late Paleozoic time. More research studies on TR are needed to extract parameters of the very early Earth-Moon system.