Shiva Linga is considered to be the formless form of Lord Shiva. It is most recognized in Shiva worship. Shivling contains both Shiva and Shakti. Worship of both makes the process complete.
There is a provision to worship different types of Shiva Lingas. Such as, Swayambhu Shivling, Narmadeshwar Shivling, Janeudhari Shivling, Gold and Silver Shivling and Parad Shivling. Of these, the worship of Aardhnareshwar Shivling is considered to be a culmination of the glory of Shiva and Shakti.