For decades, biological materials have been collected and held in museum collections, natural history collections (NHC), herbaria and environmental specimen banks (ESB). Those biological materials and accompanying data represent a potentially important source of retrospective analyses of contaminants and other chemical tracers. In ideal situations, those can provide valuable insights into changes in contaminant accumulation and concentrations over time and space. This chapter explores the benefits of such curated and catalogued specimens for contaminant research, as well as limitations and key considerations which must be kept in mind when using such samples. Three case studies examining temporal trends in contaminants using long-term biological collections are also presented.