Nuclear states with high angular momenta have in recent years been the subject of increasing theoretical and experimental interest. This is primarily due to the unique possibility such states offer of gaining new insight into nuclear structure and of testing theoretical predictions. Systematic experimental studies have become feasible due to the improved technique of exciting high-spin states in nuclear reactions induced by accelerated heavy ions. Interesting properties of such an important concept as the nuclear moment of inertia, , have thus recently been revealed in studies of the rotational bands of deformed doubly even nuclei up to spin values as high as 18-22 units of ℏ. As is well known, the value of for good rotors first grows slowly and practically linearly as the squared rotational frequency, ω², increases. Thereafter, in many cases, undergoes a sudden increase at a critical spin value, as was first observed [l] at the Research Institute for Physics in Stockholm. In some cases the nuclear rotation actually slows down, giving rise to a "backbending" or an "S-shape", in an versus ω² graph [2]. This phenomenon may be interpreted as a consequence of the Coriolis anti-pairing effect which was predicted already in 1960 by Mottelson and Valatin [3]. With increasing rotational frequency the Coriolis forces tend to break the nucleon pairs, that is, to reduce and finally to eliminate the effects of the pairing correlations. The observed behaviour of at high spin values is thus indicative of a change in the intrinsic structure of the nucleus, analogous to the phase transition from a correlated to a non-correlated state known from the theory of superconductivity.The effects of the Coriolis force acting on the valence nucleons moving in the rotating frame of the nuclear core are directly observable in odd-mass deformed nuclei. Large perturbations are observed for rotational bands when these are populated up to large spin values, that is, to as much as 33/2 or more [41] The perturbed band structure, including energy as well as dynamic properties, can be empirically well described in terms of effective Coriolis coupling matrix elements which are smaller than the theoretical ones by a factor of about 0.6-0.7 [4]. Although the Coriolis coupling mechanism is qualitatively fairly well understood, it seems that a consistent theory has yet to be formulated.High-spin nuclear states may in many cases be attributed to specific particle excitations which are remarkably pure in terms of their shell model classification, as is the case with certain multiparticle configurations in spherical and deformed nuclei at comparatively low energy. As an example the recently observed 3912 isomer in ²¹¹At at an energy of 4.816 MeV [5] can be mentioned. Due to their purity such states can be used for detailed nuclear structure studies. In particular, information has thus been gained on the effective electric charges [6] and gyromagnetic factors of the nucleons in heavy nuclei. The effective electromagnetic properties of nuclei are partially due to the polarization of the nuclear core caused by the odd nucleon or nucleons in orbitals near the Fermi level. Further polarization phenomena are caused by meson currents or by nucleon resonances in the nucleus. The nuclear polarization phenomena can be studied, e.g., through the properties of high-spin states as well as in experiments with muonic or hadronic atoms [7].The contributions to the Symposium on High-Spin Nuclear States and Related Phenomena, arranged at the Research Institute for Physics in Stockholm between May 30 and June 3, 1972, dealt with experimental and theoretical aspects of the problems mentioned above. No conference proceedings were planned, but several papers related to the general theme of the Symposium have been submitted for publication in Physica Scripta and are presented in this issue under the Symposium title.