The European Molecular Biology Open Software Suite (EMBOSS) is a high quality, well documented package of open source software tools for molecular biology. EMBOSS includes extensive and extensible C programming libraries, providing a powerful and robust toolkit for developing new bioinformatics tools from scratch. The EMBOSS Developer's Guide is the official and definitive guide to developing software under EMBOSS. It includes comprehensive reference information and guidelines, including step-by-step instructions and real-world code examples: • Learn how to write fully-featured tools guided by the people who developed EMBOSS • Step-by-step guide to writing EMBOSS applications, illustrated with functional, deployed code • ACD file development - learn how to customise existing tools without coding, or design and write entirely new application interfaces • EMBOSS API programming guidelines - quickly master application development • Wrapping and porting applications under EMBOSS - learn how to incorporate third-party tools