The main challenge in integrating legacy systems with modern applications is compatibility. Legacy systems often utilize outdated technologies, making it difficult to interface with contemporary software. This can lead to data silos, where information is trapped within the old systems and not easily accessible to newer applications. Additionally, issues such as differing data formats, lack of documentation, and the potential need for system overhauls complicate integration efforts. Businesses often face high costs and risks related to maintaining these systems while trying to adopt innovative solutions that enhance their operational efficiency.