For years I've been telling friends about the therapeutic powers of the act of writing. Now at last I have a book that I can recommend.―Judith Guest, author of Ordinary People
boring book about journal writing. A lot of it is just straightforward stuff about questions/prompts you might ask yourself in order to get started writing, or encouragement about what you might get out of it. One odd (to me) chapter at the end tells you how to get a journaling group started. I wasn't altogether sure why you'd want to get together in a group to do something personal and private such as writing in a journal.
Two qualifiers making me think my blah reaction may be a bit unfair: (a) first edition came out in 1977, and it may be that journaling was less common in those days, so pointing out potential advantages etc. would be more newsworthy; and (b) it's a book featuring instructions, and I was not actually following along and doing anything.
If you don't write a journal but want to start, you might find this book helpful and interesting. If you are just interested in reading about journaling as a technique or phenomenon, you probably won't find this helpful or interesting.
A classic and still quite useful as a basic guide to journal-writing. Includes useful information on the issue of privacy and 'what to do' with journals after they're written. I love the fact that Anais Nin stored her journals in a bank vault.