A computer-implemented method for adaptive modeling of a data stream is provided. The method may comprise receiving a plurality of data points forming part of a data stream and providing a predictive model to be fitted to the data stream. The predictive model may be a diffusion model having a plurality of diffusion parameters. A parameter estimate for each one of the diffusion parameters may be updated by obtaining a sample of at least one transition from the data stream and calculating an updated parameter estimate for the diffusion parameter by using a stochastic gradient descent algorithm on the sample. The updating of the parameter estimate may be repeated periodically or in response to one or more further data points being added to the data stream, thereby to permit adaptive estimation of the diffusion parameters of the diffusion model based on dynamics of the data stream.