These guidelines are intended to help those involved in managing fisheries to understand the range of objectives that an observer programme can meet and how these contribute towards the management of a fishery. The importance of scientific, compliance and information outputs is considered in relation to the requirements for developing and implementing management plans. The guidelines promote the use of observers as agents capable of contributing to many monitoring, sampling and compliance activities required in modern integrated fisheries management. The inputs, requirements and outputs of at-sea fishery observer programmes are presented, focusing on what they are, how they relate to the objectives of a programme and different options on how to develop them. The guidelines conclude with a design and maintenance strategy for an observer programme.