This volume presents papers from a workshop, "Advanced techniques for in situ studies of Zooplankton abundance, distribution, and behaviour" that was held during May, 1991 at Lake Lacawac in northeastern Pennsylvania, USA. The workshop focused on three advanced technologies that may be deployed in situ for studying Zooplankton: acoustic devices, the Optical Plankton Counter, and video systems. This volume is composed of three summary papers that consider the potential of these technologies, and six research reports of studies that employed some of these new tools. The summary papers (I) identify the types of questions that may be addressed with each instrument; (II) describe the design and theory of operation of each instrument; (III) describe the capabilities and limitations of each instrument; (IV) predict which limitations will be overcome in the near future; and (V) provide examples of the types of data that have been collected with each instrument. A final note compares the various devices.