When Sufism started depends on how one identifies oneself which in turn determines what one thinks Sufism is. There are many, many expressions of Sufism but it is safe to say that most believe it began as a mystical expression within the religion of Islam.

While deeply respecting all religions and beliefs, the Sufism expressed by the Sufi Movement, its teachers, leaders and participants, is drawn from the teachings of Hazrat Inayat Khan, who had this to say about it:

"Sufism has never, in any period of history, been a religion or a certain creed. It has always been considered as the essence of every religion and all religions. Thus when it was given to the world of Islam, it was presented by the great Sufis in Muslim terminology. Whenever the Sufi ideal was presented to a certain people, it was presented in such a way as to make it intelligible to those people. Sufism is neither a dogma nor a doctrine; it is neither a form nor a ceremony. This does not mean that a Sufi does not make use of a doctrine, a dogma, a ritual, or ceremony. He makes use of them at the same time remaining free from them. It is neither dogma, doctrine, ceremony, nor ritual that makes a Sufi a Sufi; it is wisdom alone which is his property, and all other things he uses for his convenience, his benefit. But a Sufi is not against any creed, doctrine, dogma, ritual, or ceremony; he is not even against the man who has no belief in God or Spirit, for a Sufi has a great respect for man...."

It is difficult to say anything about Sufism as this Sufi story from Hazrat Inayat Khan explains:

"There is a well known Eastern legend giving the idea of a soul who had found truth. There was a wall of laughter and of smiles. This wall existed for ages and many tried to climb it, but few succeeded.

Those who had climbed upon it saw something beyond, and so interested were they that they smiled, climbed over the wall and never returned. The people of the town began to wonder what magic could there be and what attraction, that whoever climbed the wall never returned. So they called it the wall of mystery. Then they said, 'We must make an enquiry and send someone who can reach the top, but we must tie him with a rope to hold him back.' When the man they had thus sent reached the top of the wall, he smiled and tried to jump over it, but they pulled him back. Still he smiled, and when the people eagerly asked, 'what did you see there?' he did not answer, he only smiled.

This is the condition of the seer. The man who in the shrine of his heart has seen the vision of God, the one who has the realization of truth, can only smile, for words can never really explain what truth means".

Much of what Pir-o-Murshid Hazrat Inayat Khan taught was transcribed from his lectures and talks given between 1914 and 1926 and are now available in a fourteen volume collection.

This link to the wonderful website of Wahiduddin Richard Shelquist presents the entire collection.

http://wahiduddin.net/mv2/index.htm

As a young man, Inayat Khan was one of the most famous musicians in India. When he came to the West, it was on the instruction of teacher, Sayyad Abu Hashim Madani, who said, "Fare forth into the world, my child and harmonize the East and West with the harmony of your music. Spread the wisdom of Sufism abroad, for to this end you are gifted by Allah, the most Merciful and Compassionate".

This unpublished lecture on Sufism is from the Nekbakht Foundation Archives and was originally published in "The Sufi" magazine in 1920. The link is:

http://wahiduddin.net/mv2/archives/sufism.htm