The "little black book" is a term for an address book, and in the simplest manner, it can merely be a small book in which you keep important contact information on friends, family and business acquaintances. The little black book more often refers to address books that can reveal information about people’s past boyfriends or girlfriends, as well as potential dates for the future. It’s linked to romance, dating, or sexual escapades. Further, occasionally a "black book" contains the names and numbers of prominent people who have engaged in certain illegal activities, like patronizing prostitutes or escort services. Some court cases, like that of the Hollywood Madam, Heidi Fleiss, deeply concerned people who had celebrity status and were listed in her little black book.

Essentially the little black book doesn’t need to be little or black. It can be a Rolodex, palm pilot, or an address book in any color. The more recent palm pilots are probably most likely to be the little black book in the modern dating/romance sense. Additionally, they’re simply practical, easy places to store contact information. The era of actually keeping a physical address book where entries are written by hand is quickly fading, as storing information becomes the work of small or larger computers. Even a cell phone with multiple capacities can be the modern little black book, whatever its intent.

With cell phones like the Apple iPhone® you don’t merely have a repository for addresses, names and numbers. You also have the capacity to email or call anyone on your list directly, simply by selecting his or her name. This certainly speeds up the process of contacting people. Further, you can use some handheld devices to access not only addresses of people but also maps to their homes should you need directions. It’s somewhat stunning what a tiny instrument like this can accomplish.

Still, some may keep a handwritten address book if they merely prefer the old manner of keeping addresses. Often the book is alphabetized, so you write addresses in each section. Some of the older style little black books have removable sheets of paper, resembling a small binder. You can buy more paper should you fill up a whole alphabet section and need more room to add additional addresses.

Others keep a handwritten address book of the old style because they prefer to keep information private, not such an easy thing to do if you someone hacks into your computer. Unlike a computer of any size, you can burn a little black book should you wish to get rid of incriminating evidence. Conversely, when your book has been a record of romantic conquests, you might have no need for it again if you are in a committed relationship.