This document specifies procedures for sampling of mesozooplankton using nets and ribbon-sampling devices in marine and brackish waters for the purpose of water quality assessment and determination of ecological status of ecosystems. Guidance on sampling procedures and the subsequent steps of preservation and storage are given. The sampling procedures allow estimates of species occurrence and their abundance (relative or absolute), including spatial distribution and seasonal and long-term temporal trends, for a given body of water. The described methods are restricted to the sampling of mesozooplankton that inhabit marine and brackish waters and exclude the shallow littoral zones which require a different type of sampling (e.g. zooplankton in salt marshes).