In DICOM, an Association is the virtual connection made between two devices (AEs) for the purpose of exchanging information.

Negotiating an Association is the first and critical step in a DICOM exchange. To create an Association, one device (the SCU) sends a list of its capabilities (abstract syntaxes and transfer syntaxes) to the other device (the SCP). Based on the reply from the SCP, the devices either establish an Association, or terminate the attempt if there are no mutually shared capabilities.

After an Association is established, the second part of the exchange (transfer of the information in question) can proceed.

Once all relevant information has been exchanged, the Association is terminated. Because no information about the Association is retained, it is not possible for DICOM devices to reference previous associations.

The DICOM conformance statement for a device specifies important information about Associations including, the length of the Association (if any) and which abstract syntax and transfer syntax will be used if the SCP supports more than one of the syntaxes proposed by the SCU.

Another important factor covered in the conformance statement is the maximum number of simultaneous Associations that are allowed. It may be necessary to purchase multiple devices to accommodate the desired number of Associations. Another factor to consider is that the more Associations that are handled at once, the more resources a device needs in the form of swap space, memory, and so on.