Collective excitations play a prominent role in nuclei away from closed shells. The onset of collectivity can therefore signal shell changes in exotic nuclei far from stability. Detailed investigations of collective excitations also allow stringent tests of state-of-the-art nuclear structure models, and in particular those bases on the mean-field approach.

Nuclear collectivity is measured by the (reduced) transition probability of the collective mode of interest, which is in most cases the quadrupole (E2) degree of freedom. Lifetime measurements are one of the "classical" methods to determine B(E2) values often used in conjunction with other spectroscopic information, such as branching or mixing ratios of the state of interest. Recent advances of methods based on the Doppler effect of the emitted gamma-radiation will be discussed, in particular their application to new energy regimes and reaction types. Coulomb excitation is an alternative yet even more powerful tool to determine nuclear collectivity as it allows in principal also to measure static moments of short lived states. While for a long time limited to stable nuclei, the availability of low-energy beams of exotic nuclei has lead to a renaissance of Coulomb excitation as means to perform detailed studies also of exotic nuclei. The lecture will show that the combination of both types of experiments allows to completely disentangle the low-energy structure of exotic nuclei and put stringent tests on their modelling using calculations beyond the mean field approach.