I just reread my underlining and notes in this excellent, but somewhat dry, scholarly book. I first read it before going to live in Indonesia. It was not very helpful in the context of Indonesia, but I found much of it to be fascinating.
It covers the entire history of Sufism, from its mysterious origins up to the present, and it does so mostly through short descriptions of the beliefs and contributions of individuals, in chronological order. This meant I did not get a very tidy and coherent understanding of Sufism, but that's all right. I did get a broad and vague sense of many aspects of Sufism, including beliefs and practices (which are not uniform across time and location). Repeatedly I was reminded of elements of Buddhism, which might seem odd.
I'll explain just briefly by saying I've read a fair number of scholarly works about Buddhism, including accounts of how certain schools or "sects" (not really the right word) came to be, as well as political influences of particular branches in China and Japan. I'm very familiar with advanced beliefs and practices, historical controversies, etc. So while I was reading Baldick's book about Sufism, I could not help but make comparisons. (Much of my understanding of religion, in general, comes from my study of Buddhism.) This does not mean Sufism is actually similar to Buddhism -- except in the respect that all religions are similar.
Baldick does mention Buddhism several times, but mostly he carefully differentiates Sufi practices (particularly the role of lodges) from early Christian practices (such as monastic communities). He also takes care to note when a particular Sufi scholar or master was at odds with, or aligned with, either Shi'a or Sunni beliefs. Overall I found this text very satisfying, and I felt a great deal of admiration for Baldick's depth of knowledge and careful research.
I certainly had much more appreciation of the emotions expressed in Rumi's verse after I had finished this book.
(The edition I read is paperback, published in 1989 by New York University Press, 208 pages. On the copyright page, it says: "Manufactured in Great Britain.")