After some general remarks, a few observed time-scale in stars discussed in this colloquium are presented. Characteristic times in stellar models for the internal structure and the outerlayers are
reviewed. Examples of mode Identification are discussed. In the low frequency domain, the situation is quite simple. But the high frequency region is more difficult to decipher as many phenomena occupy the same domain: orbital motion, rotation of a non-uniform body, spheroidal g modes and Rossby waves. The linear framework is not always relevant and the nonlinear dynamic is more difficult to characterise. In general timescales alone cannot permit a mode idenfitication. Additional informations on energy content, amplitudes, coherence, multiplicity, stationarity are necessary to discriminate among the different possibilities.