A method of encoding successive data items comprises storing history data for encoded data items, the history data indicating one or more aspects of encoding the encoded data items; encoding a given data item by a first encoding technique comprising encoding a series of zero or more data sets, each data set representing a respective range of values of the data items and selecting the series of data sets from a plurality of candidate data sets in dependence upon (i) a number of previously encoded data sets; and (ii) the history data applicable to a given property of the given data item; and encoding any remaining value of the given data item, the remaining value being an amount by which the given data item exceeds a maximum value which can be encoded by the first encoding technique, by a second encoding technique different to the first encoding technique.