||This guide is a simple, easy-to-follow reference for assessing plant parasitic nematode problems. It provides clear instructions, with many illustrations, on procedures for collecting and processing samples for nematode assessment, as well as information on accessing further identification and diagnosis support. The manual is aimed at technicians, field workers, extension agents and others with an interest in crop production and crop protection, particularly in those parts of the world where access to expert help and advanced facilities is limited. It has been produced in response to frequent demand from colleagues for a guide to aid diagnosis of nematode problems. This guide will hopefully simplify some aspects of nematology, and help to lessen the mystery surrounding this crop production problems. It is sometimes said that nematodes are viewed as a crop production problem only when a nematologist is present, and that without the nematologist there would be no nematode problem. Paradoxically, the unspecific symptoms of nematode damage are often attributed to other causes, which may seem more likely or more obvious. The reality is that a number of constraints often combine to reduce crop production, and it is necessary to quantify all of the main constraints, including nematodes. Keeping the nematode threat in perspective, in relation to other pests and diseases, is a challenge, but one that will benefit enormously from better quantification of the nematode problem through improved field and laboratory procedures. Plant parasitic nematodes are ever-present and are incidental with plant growth and crop production. They are significant constraints to sustainable agriculture and can be difficult to control. Determining the importance of individual nematode species, nematode communities and nematodes in combination with other problems is not a simple task at the best of times, but is more difficult in tropical than in temperate climates. Species previously not known to cause crop damage are continually being discovered, particularly as agriculture changes to suit changing needs, and new crops are introduced. Introduction of, or improvements in, nematological techniques and diagnostics can lead to identification of nematodes as the cause of a problem which had been present for many years, but through lack of local expertise had not been properly diagnosed. Much remains to be learned about nematodes and the damage they cause to crops. There is, for example, a lack of reliable data on the relationship between nematode numbers and yield for many different crops and types of nematodes. In many less developed countries much basic information simply does not exist. It is therefore important that even small developments and knowledge gains are recorded for future use, through publications of the relevant networks and societies, or regional or international journals. We hope that this guide will contribute to improving pest and disease management, particularly where nematological expertise is scarce, such as in the less developed countries of the world. An initial step to nematode management is establishing their presence through collection and relation with symptoms, and with expert help accurately identifying the species involved. This guide aims to support that initial step.