This depends on the type of party you’re having, who’s hosting it and, also, what type of wedding you’re planning. It used to be a “rule” that you wouldn’t invite anyone to the engagement party that you weren’t inviting to the wedding. However, these days, this rule is sometimes broken, especially if you’re having a more larger and informal engagement party or if you’re planning on getting married out of town. The engagement party can be a good way to celebrate with coworkers, etc. who may not be able to make it to your actual wedding.