This part of ISO 23611 specifies a method for sampling, handling and extracting enchytraeids from terrestrial field soils as a prerequisite for using these animals as bioindicators (e.g. to assess the quality of a soil as a habitat for organisms). Basic information on the ecology of enchytraeids and their use as bioindicators in the terrestrial environment are included in the Bibliography. This part of ISO 23611 applies to all terrestrial biotopes in which enchytraeids occur. The sampling design of field studies in general is specified in ISO 10381-1. These details can vary according to the climatic/regional conditions of the site to be sampled and an overview on the determination of effects of pollutants on enchytraeids in field situations is given in Reference [6]. Methods for some other soil organism groups such as earthworms or micro-arthropods are specified in ISO 23611-1 and ISO 23611-2. This part of ISO 23611 is not applicable for semi-terrestrial (i.e. living in or close to the pure water) soils and might be difficult to use under extreme climatic or geographical conditions (e.g. in high mountains). When sampling soil invertebrates, it is highly recommendable to characterize the site (e.g. concerning climate and land use). However, such a characterization is not covered by this part of ISO 23611. ISO 10390, ISO 10694, ISO 11272, ISO 11274, ISO 11277, ISO 11461 and ISO 11465 are more suitable for measuring pH, particle size distribution, C/N ratio, organic carbon content and water holding capacity.