If you are married, this is a must.
If you are single, I highly recommend it.
Dave Harvey's book, "When Sinners Say I Do" is by far one of the most helpful books I've ever read on the subject of marriage. Dave's writing is candid and witty, theological and sober. His personal examples are ones you can relate to and he is quick to share his weaknesses in marriage. While this book is in no way what I would call a "how to" manual on marriage, it is extremely practical - regardless of your season in life.
I wish "When Sinners Say I Do" was available in 1994, before I got married, but I am very thankful that I have it now...after 15 years!