The outbreaks of Avian Influenza H5N1 the recent years has increased our attention to a possible Pandemic Influenza. Mindful of the last century's pandemics, we fear that changes in the virus' surface antigens can cause a new virus capable of transmitting between humans. Statisticians use mathematical modelling as an instrument for predicting the pattern and intensity of the spreading of a pandemic; models can also help estimating the effects of measures such as antiviral drugs, vaccination and quarantines. Though simplified models have their limitations, it is obvious that even simple models can be a powerful tool in pandemic preparations. How should the governments and health care workers prepare for a possible pandemic? A lot of studies try to answer this, some using mathematical modelling. In this paper, I will review some of the debate on this subject. It seems to be generally agreed that we still need to learn more about influenza, and the WHO urges all countries to prepare plans for the handling of a possible pandemic. Secondly, I report the results of attempts to estimate R0-values from outbreaks of Norwegian seasonal influenza epidemics. My estimations show expected values of R0, but unexpectedly small values of latency and infectious periods. Finally, I have made an SEIR-model to simulate a possible pandemic, illustrating how differences in the viral pathogenicity and our efforts to reduce spread might alter the course of the pandemic.