The expert system discussed in this chapter, the Expert System to Software Package Selection (ESSS), was developed motivated by the needs of small bussines to support the software packages selection task. ESSS, is a rule based expert system designed to evaluate software packages using the ranking approach. ESSS evaluates software packages using six factors, and point values appropiate for each factors. The factors includes: Users requirements, technical requirements, vendor support, documentation, user considerations and costs. Tasks to ESSS developing and its architecture are showed in this paper.