Importing an existing infrastructure into Terraform is a crucial step for migrating or expanding an existing codebase, especially when dealing with complex environments. This can be achieved through the use of Terraform's `terraform import` subcommand or using third-party tools like Terraformer to automatically generate infrastructure code from an existing environment. However, simply importing resources may not be enough; it is essential to follow additional steps to ensure that the imported infrastructure is repeatable, secure, and properly configured. This includes ensuring variables are unified, explicitly declaring dependencies, randomizing names to generate unique identifiers, and securing Terraform configurations through tools like Snyk. By following these key steps, developers can create a stable and maintainable Terraform codebase that meets their organization's security and compliance standards.