CTI is the abbreviation for the technical term Computer Telephony Integration. It refers to a communications solution that, with the assistance of computer software, allows functions of the phone system to be used in conjunction with information stored in the computer system, such as phone numbers.

CTI enables control of the phone through the PC. This allows computer software such as email programs to connect you to the telephone system with just the click of a mouse. With incoming calls, a corresponding CTI function can display information about the caller from a CRM system, such as their contact details or call history. These additional functions make communication in business more efficient and allow for the better exchange of information.

To operate Computer Telephony Integration, the computer needs the appropriate software to control the system phone or communicate with the telephone system. Many PBX manufacturers offer such software solutions for their devices. To facilitate the connection of CRM or back-end systems with as little effort as possible, the CTI programs usually have software modules that can communicate with popular CRM and back-end systems via standardised interfaces.

For communication between the telephone system and the computer software, there are standardised protocols such as CSTA (Computer Supported Telecommunications Applications). This protocol defines the type and format of the data to be transmitted without specifying the actual transport layer, thereby allowing CTI solutions to be implemented by many more manufacturers.