Customer integration has many recognized advantages, but also entails negative side effects that may impair the success of innovative activities. These negative side effects have not yet been sufficiently investigated. Whereas some may occur within the entire early innovation phase, others are likely to affect only few sub-phases. Each sub-phase, defined in a slightly new way as compared to existing models in order to meet the investigation subject, has different activities and aims and therefore requires special integration methods and customer types. Based on extensive research and empirical studies, the paper illustrates different integration methods, negative effects of customer integration, and measures to avoid them.