ISO 21018-1:2008 specifies methods and techniques that are applicable to the monitoring of particulate contamination levels in hydraulic systems. It also describes the relative merits of various techniques so that the correct monitor for a given application can be selected. The techniques described in ISO 21018-1:2008 are suitable for monitoring the general cleanliness level in hydraulic systems, the progress in flushing operations and support equipment and test rigs. ISO 21018-1:2008 can also be applicable for other liquids (e.g. lubricants, fuels and process liquids).