The Third Party Annotation (TPA) project collects and presents high-quality annotation of nucleotide sequence. Annotation is submitted by researchers who have not themselves generated novel nucleotide sequence. In its first few years, the resource has proven to be popular with submitters from a range of biological research areas. Central to the project is the requirement for high-quality data, resulting from experimental and inferred analysis discussed in peer-reviewed publications. The data are divided into two tiers: those with experimental evidence and those with inferential evidence. Standards for TPA are detailed and illustrated with the aid of case studies.