Many of the classic Visual Basic 6 applications are not ready to jump on migration to the .Net world so in this situation any enhancement or up-gradation to these applications is like a nightmare to fulfill business requirements.
COM interoperability features provided by the .Net framework work as a remedy in this situation without changing or upgrading the existing application. Complete cost in terms of both resources and time of a full rewrite of the application can be prohibited. Enhanced UI Interop user controls can be developed in .Net and can be used in VB6 form.
Component object model (COM) interop is one of the interoperability mechanisms that the .Net common language runtime (CLR) offer. This enables to interact the unmanaged code to managed code.