An address book is a book in which contact details (e.g. address, telephone number, e-mail address, fax number, mobile phone number) are kept. Details are normally stored in alphabetical order of people's names, although when this is done on paper, entries can easily end up out of order as more individuals are added or as people move. Many address books are small ring binders that allow pages to be added, removed, or shuffled around in order to make room.

A related term that has entered the popular lexicon is little black book (or simply black book). Such books are used as dating guides, listing people who the owner has dated in the past or hopes to in the future. More explicit variations are guides for sexual encounters. It is unclear how prevalent this is in practice, though such books have been mentioned in many pieces of popular entertainment.

Software address books

Address books can also appear as computer software designed for this purpose, such as the Apple Address Book. Simple address books have been incorporated into e-mail software for many years, though more advanced versions have emerged in the 1990s and beyond. A personal information manager (PIM) integrates an address book, calendar, task list, and sometimes other features.

Entries can be imported and exported from the software in order to transfer them between programs or computers. The common file formats for these operations are:

• LDIF (*.ldif, *.ldi)
• Tab delimited (*.tab, *.txt)
• Comma separated (*.csv)

Individual entries are frequently transferred as vCards (*.vcf), which are roughly comparable to physical business cards.

See also

• Rolodex