This paper reviews the rich corpus of observational evidence for tidal
effects, mostly based on photometric and radial-velocity measurements.
This is done in a period when the study of binaries is being
revolutionized by large-scaled photometric surveys that are detecting
many thousands of new binaries and tens of extrasolar planets.
We begin by examining the short-term effects, such as ellipsoidal
variability and apsidal motion. We next turn to the long-term
effects, of which circularization was studied the most: a transition
period between circular and eccentric orbits has been derived for
eight coeval samples of binaries. The study of synchronization and
spin-orbit alignment is less advanced. As binaries are supposed to
reach synchronization before circularization, one can expect finding
eccentric binaries in pseudo-synchronization state, the evidence for
which is reviewed. We also discuss synchronization in PMS and young
stars, and compare the emerging timescale with the circularization
We next examine the tidal interaction in close binaries that are
orbited by a third distant companion, and review the effect of
pumping the binary eccentricity by the third star. We elaborate on the
impact of the pumped eccentricity on the tidal evolution of close
binaries residing in triple systems, which may shrink the binary separation.
Finally we consider the extrasolar planets and the observational
evidence for tidal interaction with their parent stars. This includes
a mechanism that can induce radial drift of short-period planets,
either inward or outward, depending on the planetary radial position
relative to the corotation radius. Another effect is the
circularization of planetary orbits, the evidence for which can be
found in eccentricity-versus-period plot of the planets already known.
Whenever possible, the paper attempts to address the possible
confrontation between theory and observations, and to point out
noteworthy cases and observations that can be performed in the future
and may shed some light on the key questions that remain open.