Indian Classical Music is probably the most ancient form of world music and it dates back to Vedic Age. The time of this age is debatable but most of the historians commonly agree that it started from 2000 BCE. Hindus believe that the creation was started with a indistinct sound which later manifests itself as a two note sound,OM( It originates from the tonal frequency and eventually rises upto the perfect fourth.) and then everything happened from that divine sound. This itself proves how old the connection of music was with the Vedic civilisation.
Vedic literature was preserved in a verbal form for many years. Therefore Vedas are known as "Sruti". The similar trend has also permeated into the musical culture and that's why it doesn't have any staff notation for many years until the great scholar Vishnu Narayan Bhatkhande introduced his notation system in early twentieth century. The whole learning process of Indian Classical Music depends on a great teacher-student relationship where a student stays at his guru's house for years and learn the intricacies and technical nuances by heart and then when he matures enough, he starts performing under a king's patronage. At still matured age, when he feels like he has got enough grasp on his music that he can teach, then he starts taking students and continues the legacy, the "Parampara". During the whole process no written dossiers are used and that is one of the reasons why the history of Indian Music is so difficult to decipher and understand fully.
Now let us delve into some of the basic features of the music itself. The most striking difference as compared to Western Classical would be the lack of harmony and orchestration in Indian Music. It has always been a solo performance where a vocalist or a instrumentalist play the melody with a percussionist and a drone of two basic notes is played by one of the students.