A method of determining the position of a radio signal transmitter (50, 51) comprising: determining the type of radio signal being transmitted from the radio signal transmitter (50, 51) by analysing the radio signal for radio signal characteristics; and correlating different sets of information in a way dependent on the determined radio signal type in order to determine the position of the radio signal transmitter (50, 51); wherein each set of information corresponds to a different relative position of at least one receiver (1, 2, 3) to the radio signal transmitter (50, 51), each set of information comprising: radio signal data derived from radio signals received by the at least one receiver (1, 2, 3) from the radio signal transmitter (50, 51) at each respective relative position; and positioning data containing information about the position of the at least one receiver (1, 2, 3) at each respective relative position, wherein the method further comprises assessing the dynamics of a platform on which the radio signal transmitter (50, 51) is supported, and correlating the different sets of information in a way dependent on the determined dynamics of the platform, and characterised in that determining the type of radio signal being transmitted from the radio signal transmitter (50, 51) comprises determining whether the radio signal originates from a radio signal source of a type that is mobile or a radio signal source of a type that is stationary, and if the radio signal originates from a radio signal source of a type that is mobile, repeating the step of correlating different sets of information to track the radio signal source that is mobile, and wherein determining whether the radio signal originates from a radio signal source of a type that is mobile or a signal source of a type that is stationary comprises: storing in a database a set of rules and assumptions that may be made about radio signal sources of different types, analysing the radio signal characteristics of the radio signal, consulting the database, and thereby inferring the type of radio signal source. determining the type of radio signal being transmitted from the radio signal transmitter (50, 51) by analysing the radio signal for radio signal characteristics; and correlating different sets of information in a way dependent on the determined radio signal type in order to determine the position of the radio signal transmitter (50, 51); wherein each set of information corresponds to a different relative position of at least one receiver (1, 2, 3) to the radio signal transmitter (50, 51), each set of information comprising: radio signal data derived from radio signals received by the at least one receiver (1, 2, 3) from the radio signal transmitter (50, 51) at each respective relative position; and positioning data containing information about the position of the at least one receiver (1, 2, 3) at each respective relative position, wherein the method further comprises assessing the dynamics of a platform on which the radio signal transmitter (50, 51) is supported, and correlating the different sets of information in a way dependent on the determined dynamics of the platform, and characterised in that determining the type of radio signal being transmitted from the radio signal transmitter (50, 51) comprises determining whether the radio signal originates from a radio signal source of a type that is mobile or a radio signal source of a type that is stationary, and if the radio signal originates from a radio signal source of a type that is mobile, repeating the step of correlating different sets of information to track the radio signal source that is mobile, radio signal data derived from radio signals received by the at least one receiver (1, 2, 3) from the radio signal transmitter (50, 51) at each respective relative position; and positioning data containing information about the position of the at least one receiver (1, 2, 3) at each respective relative position, wherein the method further comprises assessing the dynamics of a platform on which the radio signal transmitter (50, 51) is supported, and correlating the different sets of information in a way dependent on the determined dynamics of the platform, and characterised in that determining the type of radio signal being transmitted from the radio signal transmitter (50, 51) comprises determining whether the radio signal originates from a radio signal source of a type that is mobile or a radio signal source of a type that is stationary, and if the radio signal originates from a radio signal source of a type that is mobile, repeating the step of correlating different sets of information to track the radio signal source that is mobile, and wherein determining whether the radio signal originates from a radio signal source of a type that is mobile or a signal source of a type that is stationary comprises: storing in a database a set of rules and assumptions that may be made about radio signal sources of different types, analysing the radio signal characteristics of the radio signal, consulting the database, and thereby inferring the type of radio signal source. storing in a database a set of rules and assumptions that may be made about radio signal sources of different types, analysing the radio signal characteristics of the radio signal, consulting the database, and thereby inferring the type of radio signal source.