Erik Lindström A Delayed Propagation Filter for Partially Observed Diffusion Processes Abstract We develop a sequential Monte Carlo filtering algorithm for non-linear, partially observed diffusion processes. The filter behaves advantageous compared to the ordinary particle filters (i.e. the Bootstrap filter) when the measurement noise is small, as the approximation does not degenerate. The performance of the filter can be improved by applying importance samplers. Several importance samplers for partially observed diffusions are derived, including a near optimal importance sampler. The samplers can be used in ordinary particle filters as well as in the proposed filter. The performance of the near optimal filter is competitive over a large range of different parameter values. This talk is based on joint work with Hans R. Künsch, ETHZ