Population fluctuations have been a long-standing interest of ecologists. Although the subject is old, it has often provided new insights. Recent studies concerning population fluctuations include the following new topics: (1) new methods for detecting density-dependence and population regulation, or time series analysis for detecting chaotic fluctuations; (2) spatially explicit models of population fluctuation; (3) dynamics models in stochastic environments; (4) the effects of individual differences and local interactions on population fluctuations; (5) evolutionary ecological approaches to dynamics; (6) dynamics in multispecies communities; (7) theories of extinction in conservation biology. In addition to these recent interests, many ecological and evolutionary studies cannot ignore population fluctuations since they affect or are affected by many ecological and evolutionary processes. The main purpose of this symposium session was to argue what problems concerning population fluctuations are unsolved and worthy of pursuit, and to discuss how and to what extent ecological and evolutionary researches should take aspects of population dynamics into account. Six speakers presented lectures on the following topics (an asterisk indicates a speaker who added a coauthor for the article in this special feature): 1. P. Turchin (University of Connecticut): Nonlinear time-series modeling of vole population fluctuations. 2. M. Tuda (University of Tokyo): Temporal and spatial structures and dynamical properties of populations. 3. M. Nakaoka (University of Tokyo): Dynamics of field populations under fluctuating environments. 4. Y. Harada* and Y. Iwasa (Kyushu University): Dynamics of density and local crowding in a lattice structured population. 5. T. Hara (Hokkaido University): Individual variations and growth dynamics in plant populations. 6. J. Yoshimura* and V. A. A. Jansen (Imperial College at Silwood Park): Population dynamics and evolution in stochastic environments. Each topic by each speaker was related to the new topics mentioned above. The lectures by P. Turchin and M. Tuda are related to time series analysis (topic 1), that by M. Nakaoka to dynamics in changing environments (topic 3), by Y. Harada to spatial structure (topic 2), by T. Hara to individual differences (topic 4) and that by J. Yoshimura to evolutionary ecology (topic 5). Of the six lectures, five appear in this volume. The 17th symposium of the Society of Population Ecology was held from September 30 to October 2, 1995 at Yunoyama-onsen in Mie Prefecture, Japan. There were two sessions in the symposium. The first was “Population fluctuations,” which resulted in this special feature, and the second was “Interactions among microorganisms, animals and plants,” which appears in another special feature of this volume. We would like to thank the speakers for their interesting lectures and for submitting papers to this volume. The committee of the symposium is very grateful for the financial support provided by the Japanese Society of Applied Entomology and Zoology for inviting Peter Turchin, and the financial support provided by the of the Society of Population Ecology for inviting Jin Yoshimura.