PBX may refer to:

• Polymer-bonded explosive
• Pre-B-cell leukemia homeobox
• Private branch exchange, a telephone exchange that serves a particular business or office
• PBX, a rewrite of the Project Builder IDE

A business telephone system is any of a range of a multiline telephone systems typically used in business environments, encompassing systems ranging from small key systems to large scale private branch. A business telephone system differs from simply using a telephone with multiple lines in that the lines used are accessible from multiple telephones, or "stations" in the system, and that such a system often provides additional features related to call handling. Business telephone systems are often broadly classified into "key systems", "hybrid systems", and "private branch exchanges".