The SEISAN software package for processing of earthquake data has been in use for 30 yr. SEISAN is a collection of programs that help to carry out tasks from the basic processing at a seismological observatory to more advanced seismological research. During its history, the software has been adopted to different hardware and operating systems. However, the core of the software with a folder‐ and files‐based database and event‐based processing has remained stable. The main focus in the design and development of the software has been the efficiency in data processing for the user. The software comes with manual, tutorial, and training exercises. This together with regular training activities has made SEISAN a useful tool for many observatories around the world.